All right, lemme lay out the full logic here.
If you remove Illusion from the equation, you are missing some information, but you can make reasonable inferences based on the information you do have available. Ignoring Protean as well, Alakazam is going to be a Special attacker that prefers Psychic moves, and it's going to avoid stall-y sets that rely on bulk because it can't pull them off. (And if it tries one, well, there you go, you have the advantage) Any non-Psychic move is coverage, not its primary attack, and Physical moves are sub-optimal. (Albeit it's conceivable an Alakazam set might appreciate something like Focus Punch for Chansey, like in Gen III) This in turn tells you a lot of things: it probably doesn't have priority, and if it does have priority that's actually worth commentary, that priority is Vacuum Wave, as it's either that or Prankster Nature Power off of Whimsicott. fair enough assuption. zam runs special attacks, and in return, you can be somewhat safe while facing it knowing such a factor is true.
So you can be confident that Special walls, particularly those immune to Psyshock/Psystrike are reasonable effective against Alakazam builds. (If it's running Secret Sword, that means it's running Keldeo, which gives it no proper STAB, among other problems) You also know its Speed tier: skipping over the question of Mega Alakazam for the moment, you know for a fact what can and cannot outspeed it on your team, barring Scarf, and if it's Scarfed then you will learn that and know that it's limited and going to switch a lot.yes, zam is naturally really fast, so enless you run hyper offense, chances are you will either be relying on priority, or a bulky attacker to take it down.
You know that Alakazam takes tremendous damage from Shadow Sneak and Sucker Punch, and only the latter cares all that much about questions of build. (eg Vacuum Wave Alakazam, particularly backed by Nasty Plot, could potentially defeat a Sucker Punch-based counter unexpectedly) again, true, you know that zam has a massive weakness to 2 priority moves.
You know that Alakazam is too fragile to put up a Substitute capable of tanking a Seismic Toss/Night Shade.
You know that its Special bulk is actually decent, so you might want to avoid focusing too much on that.
You also will be tipped off to a lot of specific builds instantly: if it's GeoZam, the Fairy Aura is a blatant signal. If it's some kind of Mold Breaker build, you'll be warned of that too. If somebody decides Primordial Sea Alakazam has a niche, you'll be forewarned. yes. straightforward stuff here.
You won't, at first glance, know what Alakazam's item is (Unless it announces itself, like Air Balloon), you won't necessarily know what Ability it has (Again, unless it announces itself), and you won't know its exact four moves, but you can eliminate vast swathes of possibilities by virtue of them being so sub-optimal that if the opponent is doing one of them making a mistake based on "Well, actually it is a Physical Alakazam" is likely irrelevant and easily recovered from, and the terribleness of the build in turn exploited. yes, this is true with every pokemon. moreso then in other metas.
Then we add Illusion in.
Now, you know nothing about what Alakazam is. You have only the certainty that the Alakazam in front of you has to be one of the six members you can see on the enemy team, which is fairly limited in utility if they haven't done something silly like make a mono-Psychic-Special-Attacker team. ok...
Now, your decision-making process can go one of two ways, as I laid out before.
In the first scenario, you assume everything is non-Illusion until you hit a blatant Illusion. (eg Gengar using Knock Off to OHKO a bulky mon well outside of Gengar's ability to Knock Off to death) In this case, Illusion is basically uncompetitive bullshit you are incapable of accounting for and doing anything about until after it has likely cost you a Pokemon. "Virtually guaranteed to KO at least one enemy team member" is not an acceptable trait in Smogon metas.except suprising your counters is a normal thing in competative pokemon, and it is common for pokemon to run suprise sets to catch their usual counters off guard. what makes this any different from protean landorus T and aerialate landorus T? both can pick off eachothers counters and checks, and it ALSO will cost you a pokemon. altaria in OU runs its special set SPECIFICLY to catch its physical set walls off guard. guarenteed kos on at least one member is also a common thing i dont even know what you are saying. its not like every game is a 6-0 fest. "mon for mon" is a common thing in the metagame, and even vs stall, losing one member is rather common. what are you even saying here.
In the second scenario is that you assume anything and everything is Illusion until proven otherwise. You know what that decision-making process looks like? Honestly, it's basically random: again, unless the enemy team has a sharp bias in its team design, any decision can be the wrong decision because fuck you the thing in front of you is an Illusion, and conversely you making a decision on the possibility that it's an Illusion can be the wrong decision because it isn't.
No RNG steps in to feed you misses and unexpected Burns, but player skill is largely ripped out of the equation, because players are incapable of making even marginally informed decisions. It's indistinguishable from "randomness caused by dice programs". It only gets worse if both sides have Illusions up: they're both making completely mis-informed decisions, with no ability to predict or account for their opponent's actions because they have no information.so what your saying, is its uncompetative because you have no indication when something is illusion or not. well, we should ban EVERYTHING this meta offers, since NOTHING is set in stone in this meta. illusion is not uncompetative like shadow tag, swagger, or moody. its not based around dice rolls, or tilting matchups in your favor, its built around suprising stuff. which is a COMMON THING IN EVERY METAGAME. and is a COMMON THING IN THIS META.
It's functionally random. Bye-bye player skill, same as any match decided by crits or misses or lucky Burns.if you seriously lose a game because one of your pokemon is dead. then really i question your teambuilding. enless you run stall, illusion should NOT determine your game, because you still have 5 other pokemon capable of revenge killing it. as much as i hate to be that guy, but if you DO run stall, and thats why your upset about this, you really just have to accept your losses. its not that i dislike stall, i LOVE a good stall match, its just this entire meta follows a similar "beat your counterS" formula, so stall REALLY has difficulty working in this meta as is.
Note, in particular, that the first definition you've provided -success or failure brought about by something other than one's actions (choices, in this case)- applies fully to having Illusion a part of Inheritance. You don't succeed or fail based on doing your best while your opponent does their best and failure on your part reflects a poor decision-making process, whether at the team level or at the match level: you succeed or fail based on how your decision-making process happens to coincide with or diverge from the Illusion's impact on the situation. If you make decision A and it happens to work in spite of the Pokemon you're facing being completely different from what you thought it was, that's luck. If you make decision B, and it happens to fail because the Pokemon you're facing is not what you thought it was, with zero ability to anticipate the possibility in a meaningful way, that's luck.
do you not know what chance means? the one guy is right, you just put words into my mouth, the official definition is "success or failure apparently brought by chance rather than through one's own actions." chance-"a possibility of something happening." this isnt illusion, because the illusion user has control over illusion. its not a "possibility" of illusion happening. i get what your thinking, that "illusion is chance due to it being unpredictable" but thats not what its trying to say, it means it in a "roulette" sort of way, a "nobody can predict the outcome" which is false. since the illusion user KNOWS he has illusion. it falls into the second catigory. NOT the first one.