I love the PvP idea because we used to do that with NWN, where we would compete in Pvp arenas and I really got to see firsthand the combat weaknesses of 3.5 edition in regards to class versus class.
The top two classes in terms of strength were Sorcerer (Sor 17/Monk2 /Pally 1) and Barbarian because they excelled at their primary way of causing damage and could protect themselves fairly well. It showcased to me for the first time how unbalanced the classes were in 3.5 when in a combat encounter with each other.
I'd love to be able to do the same with the existing builds - standard equipment - just to see who ends up being strongest on the class balance perspective at a level per- level basis. No barrelmancy, no throwing people of course.
My multiplayer groups have already done a certain amount of that but nothing conclusive except that the Dire Raven is incredibly OP as a pet. Ranger with a Bow and a Dire Raven will usually win.
Base 5e is a bit more balanced in between classes than 3.5e in my opinion (4e is actually the most balanced imo strangely enough) but there are still combos that are absolutely devastating if you are thinking in terms of PVP.
Warlock Eldritch Blast with Agonizing Blast is potentially one of the most devastating multi attacks possible with 4 separate attacks (that can crit) that can all do 1d10+5 damage, push/pull, and slow from 300 feet away with the damage type that is the hardest to get resistance for. So a warlock with one cantrip (if all 4 hit which is likely) can do (without even calculating crits) at minimum 24 Force Damage, at maximum 60 force damage, and debilitate the opponent while the opponent is not even close.
Staying on warlock, Pact of the Chain can also be very nasty with the newest update of Tasha's. You can Flock of Familiars out 3+ imps, pseudodragons, quasits, or sprites that can all grant advantage, take hits, inflict status effects like fear and poison, and be hard to kill with magic (with also being able to be granted resistance to an attack so they survive.)
A fighter or monk with with polearm mastery, sentinel, and mage slayer can lock down any character with opportunity attacks by just standing there menacingly, combine with a high AC and bonus to saving throws and they are nearly impossible to deal with 1 on 1.
Three levels of any class that can cast darkness and the feat that gives an eldritch invocation (or better just warlock again, my favorite class lol) to give devil's sight is absolutely nasty, so put this on a rogue and watch the sneak attack dice fly, especially assassin rogue that essentially will crit every turn because of this.
And I could go on about absolutely overpowered combinations, but uh my point here is there are many that can be absolutely nasty in PVP and generally every class has something they can do or get that can snowball into power. (Just the combos I know the best are warlock,cause I love the Invocations and the modularness of the class with them and the pact boon.)