I don't think it's necessarily only those two options. There's probably an understanding that only more serious Pokémon fans will buy the third versions of each generation, while the first versions are for a wider audience which includes casuals and kids. So they make movesets easier in the first games, and then give things a little difficulty spike in the third versions because the players tend to be better. Which is still unnecessary, kids can figure out how to win third versions easily too, but it's a less cynical explanation for things.Even if the enhanced version movesets are significantly better, that brings up a whole new problem. Either dev conditions and/or priorities for the first versions are just so buggered that they can't even properly design the bosses' movesets on the first go or they're deliberately gimping them as yet another push for people to buy the third versions, both of which are very bad for different reasons
I think the difference, which Codraroll also identified, is that whether something actually is particularly challenging or not, what matters is whether it feels challenging and therefore rewarding. Elite Four members having only 4 Pokémon makes them feel like regular trainer battles, and I think that's what Samtendo means by battles becoming monotonous. When boss battles of recent gens feel tonally like trainer battles of older gens, players don't get that little dopamine rush of feeling like they actually achieved something. This is something SwSh does well, because the atmosphere of gym battles is so damn good that it feels like an achievement even though the battle's easy, and the Elite Four (or Champion's Cup) are actually 6v6 battles right? This is basically all we've been asking for.This is something I hear often, it having "become" this way or heavily changed, and I don't aree. Gym leaders have been filled with gunk Pokemon and movesets since Gen 1. Even late-game. I figure Gen1 and Gen2 don't need that much elaboration (Sabrina Abra lol), but...
R/S Leader(s) 7 has two Pokemon total, and for a double battle no less.
R/S Leader 8... Seaking is neither the worst nor the second worst out of 5. Luvdisc and Sealeo get those honors.
D/P Leader 7 has Snover and Sneasel.
B/W Leader 7 has Vanillish. No leader in the whole game has more than three Pokemon.
All of these Pokemon are worse than any 6-8 XY leader's Pokemon. Sure, Wulfric gets obliterated by any Fire-type, but so does B/W Brycen, unless you fall before the might of... Beartic's Brine.
This may have not been what you meant, but a lot of people point to the "better strategies" and "complete movesets" of Pokemon from earlier generations, and, well...
Winona (6) has Water Gun / Supersonic / Aerial Ace (50 Atk!) / Protect Pelipper. Send help, please. Skarmory has Sand-Attack and Fury Attack.
All of Wallace's (8) Water-types have Water Pulse and no stronger STAB move (besides Earthquake Whiscash, which is admittedly good stuff). Luvdisc has Flail, Milotic has Twister (covers Dragons? it has Ice Beam. Twister just free reprieve chance), and Seaking has Fury Attack. All free-turn filler.
Candice's (7) Sneasel has Avalanche (???) and Slash. Snover has Razor Leaf and Ingrain (sure it'll survive to take advantage of that). Abomasnow has Swagger and Grasswhistle?? Like sure, those two can be dangerous, but this is clearly cheese and not a competent moveset for rewarding play.
Volkner's (8) Ambipom has no STAB moves. Raichu and Luxray have Charge Beam but no other special moves. Octillery has no move above 65 BP, which includes 10 BP Bullet Seed.
Skyla (6) has all-physical Swoobat with 57 Attack. Not technically all-physical because... Amnesia? (not Simple.) Unfezant has Quick Attack, Razor Wind, and Leer.
Brycen (7) has Astonish Vanillish, Rapid Spin Cryogonal, and Swagger Beartic.
B/W Drayden/Iris (8) have two Dragon Dance sweepers! With, uh, Dragon Tail as their only STAB move. What? And Fraxure has Dragon Rage.
"Why are you only using the first entries and not Emerald/Plat/B2W2?" Because X was a first entry too. There may be a case that remake trainers are notably better than first entry trainers, but that's not the narrative I normally hear.
Even if the movesets suck and the champion uses a Delibird, if bosses just used more Pokémon the games would be way more fun. Players tend to have 6 Pokémon on their team by the mid-to-late-game, so when the Elite Four or 8th gym leader also uses 6 Pokémon it feels like you actually achieve something when you beat them as opposed to entering the battle with the upper hand. I think gyms should be structured as 1 uses 2 Pokémon, 2 and 3 use 3 Pokémon, 4 and 5 use 4 Pokémon, 6 and 7 use 5 Pokémon, and after that every boss uses 6. Yes, that probably includes the battle against the evil team leader, though 5 is also fine (Platinum Cyrus).