OM! Like I said before, I'd personally shove Deoxys-A into the D-umpster rank due to the sheer amount of team support it needs and then either a Focus Sash or even more team support. On top of this, it's typing is rather unremarkable and only notable because moves like Psycho Boost, Psystrike, and Photon Geyser are so strong. I'd settle for C-rank of sorts, but I lean on D.
Phera at least has a rather relevant STAB and has almost not competition as either a Bug or a Fighting type. Its typing is the only reason why I'd rank it higher, personally, because otherwise it shares a number of Deo's problems. I dunno if its worthy for C-rank either, but I've not run Phera since CFZ meta, so all I can really judge is by the Phera's I've encountered that have done dick-all to me. Granted, my teams usually aren't of the type that Phera can prey on.
Also, on the whole Hustle thing, now that I think of it, why are you not doing Hustle MMX instead? You get more power, more bulk, more move choice freedom, more item choice freedom, and an improved STAB combo at the cost of speed and the picking up of some weaknesses that don't matter because Deo-A bulk might as well be weak vs all. You're not using your special attack, so you're not using Deo-A's mixed capabilities, which is the main reason to run it over MMX/Y. MMX can even theoretically get away running Coil too to deal with Hustle's problems, provided you deal with the Spectral Thief users first.
But then Gengar, Greninja-Ash, MMY, Sceptile, etc. can outspeed (or speedtie) and potentially 1HKO MMX.
MMX is better for Contrary because it can stay alive thanks to V-Create, and boost via Psycho Boost, but I think the main reason for Hustle is the Speed, and surprise factor (it lures in walls that you can 1HKO). Further, MMX is almost obligated to run Close Combat (or Superpower on Contrary), which can lead to 4MSS.
It’s not that MMX is bad, (for Speed though one could argue that is too big a factor), but MMX would likely have the advantage over D-A if it, like you said run different moves, which leads to would it give up Fighting STAB for the same moveset?
I think MMX would be better off as a Contrary user where it can boost its Attack with Superpower to gain a Hustle equivalent, and stay alive with V-Create.
Deoxys-A is more about immediate Speed and Attack so it wouldn’t want or need Contrary for the physical side (maybe special like Psycho Boost), and thus I feel like Deoxys-A isn’t outclassed because MMX’s advatages lie in STAB it wouldn’t use anyways and if it uses Hustle and Coil, then 4MSS due to having 1 less coverage move.
If it had the exact same moveset, then it couldn’t always KO (due to going 2nd) Sceptile-Mega, MMY, Gengar-Mega, Greninja-Ash, opposing MMX, etc. which is part of the whole reason to use Deoxys-A, while they could all 1HKO MMX.
As for Pheromosa, I would argue MMX outclasses it as a Fighting Type (let’s be honest the only Faster than MMX Pokemon weak to Fighting is Greninja-Ash and Lopunny-Mega) because it outspeeds all other Pokémon weak to Fighting harder and can survive thanks to Contrary (Superpower).
Pheromosa has some competition from Scizor-Mega, as well as Triage Heracross for Bug moves. Heracross can also provide competition for Fighting moves:
252+ Atk Life Orb Triage Heracross-Mega Drain Punch vs. 252 HP / 252 Def Registeel: 273-322 (75 - 88.4%) -- guaranteed 2HKO after Leftovers recovery
Pheromosa with Adamant:
252+ Atk Pheromosa Close Combat vs. 252 HP / 252 Def Registeel: 266-314 (73 - 86.2%) -- guaranteed 2HKO after Leftovers recovery
Still weaker
Jolly:
252 Atk Pheromosa Close Combat vs. 252 HP / 252 Def Registeel: 242-288 (66.4 - 79.1%) -- guaranteed 2HKO after Leftovers recovery
Even weaker
(Pheromosa typically doesn’t carry Life Orb in Pure Physical sets because Dazzling sets and Skill Link sets use Focus Sash or King’s Rock, respectively).
Bug Typing doesn’t really hurt Grass Types because the ones used are neutral (Venusaur-Mega, Kartana, Ferrothorn) besides Sceptile-Mega, and the same goes for half of the Psychics used (Solgaleo, Dusk-Mane, Dawn-Wings, Lunala, MMX, Lugia). Against Dark Types, Fighting is typically better (Tyranitar-Mega), or the same (Yveltal, Gyarados-Mega, Greninja Ash).
Also, Lopunny does offer some competition for Focus Sash Reversal Sets, due to Flail STAB and Spectral Thief Immunity.
(I.e. Flail, Reversal, Shell Smash, Spectral Thief/V-Create) and can run either Dazzling with V-Create (Aegislash) or Scrappy with Spectral Thief (anti-sweeper Check).
Regardless. I see your points and they are pretty valid, just a few technicalities on what sets them apart.
