All jokes aside getting the full rundown on what 621 can do would be nice (even though I'm almost certain that he wins)
The main stuff was already covered but there's also the skill 621 has which is insane and should be mentioned
621 is a stupidly skilled AC pilot with a "fried brain" (said by Walter in the first mission) to a point where 621 canonically cleared each route (Or at least in Alea Iacta Est) with LOADER 4 (Seen in the A.I.E. end cutscene), arguably the lowest quality AC in the game next to MAD STOMP. 621's skill is enough that ALLMIND with the arena evaluation and analysis programs used 621 as a reference for improving its AI enough to take on Carla and Walter successfully in the 2nd to last mission of the A.I.E. route
The most worthwhile things to point 621 beat is Balteus (autonomous PCA weapons platform), a C Spider (autonomous coral weapon), multiple PCA warships, LC / Light Cavalry + HC / Heavy Cavalry mechs (All "cutting edge" technology , the Ice Worm (Another coral weapon, with 621 needing the stun needle launcher to break through its shield and Carla's big railgun thing to incapacitate it after the shield goes down), the PCA enforcement system defenses as a whole, IB 01 CEL 240 (An incredibly fast, aggressive, and well armed autonomous coral weapon)
Then for route exclusive stuff (Fires of Raven, Liberator of Rubicon, and Alea Iacta Est which will abbreviated with FOR, LOR, and AIE)
FOR: V.I Freud (Top 1 other AC pilot in the Arena, also unaugmented and just a dude that likes fighting), a ton of PCA worships Arquebus Corporation took, V.IV Rusty in Steel Haze Ortus (Extra high quality AC made as a collaboration between Elcano Foundry and Furlong Dynamics to help the Rubicon Liberation Front that makes use of schenider ac details, elcano weapons, the laser slicer melee weapon, and a bullet orbit), and lastly Ayre using IB SOL 644, the largest and strongest bipedal non piloted c weapon in the game (Ayre does crazy stuff with it including what looks like teleporting, high speed rushes, a jet mode that can ram for huge damage and send 621 to the upper area limit of the mission, and seemingly using coral spirits to attack)
LOR: 621 overcomes Carla's prepared ambush + lock in trap, Chatty + Carla together, Arquebus Balteus (Piloted by V.II Snail, referred to by Rusty as "second to none", Arquebus Balteus can do constant large plasma shots, hugely powerful laser shots, some missiles, pulse shot bursts, assault armor + pulse armor like normal Balteus, and a massive sweep of plasma to a point where it's like a sea on the ground for a moment), and lastly Handler Walter in HAL 826, a c weapon that's a pilotable AC. Note that Walter (with Carla) was holding out against ALLMIND's 6 vesper copies until ALLMIND joined in
AIE: Not a fight but 621 got around Chatty trying his hardest to prevent 621 from overcoming the Xylem's system's. In the last mission (of the entire game), 621 beats MIND BETA alongside the 6 vesper copies, after that 621 (with Ayre in ECHO helping) then takes on an adjusted IB SOL 644 with 2 adjusted C Spider's by ALLMIND (With G5 Iguazu mainly in control) until at the halfway point where ALLMIND Iguazu gets so pissed and angry with envy that a coral resonance burst destroys the c spiders, ECHO, and boots Ayre from anything at the moment, with Iguazu getting extra aggressive in this phase, constantly melee rushing with only occasionally doing rapid laser fire
TL;DR: 621 is stupidly skilled at what he does. Reminder that all of that was done with a top 5 worst preset AC's in the game and canonically basically a walking museum exhibit junk mech (Including 621's gen 4 augmentation, which gets commented on in Defend the Dam Complex mission by Chartreuse, the top 5th pilot in the Arena)
Also two minor notes; Coral weapons ignore defenses (at least in game) and AC 6 scaling can't be applied to previous games since it's a new continuity
