On the contrary, solely based on gameplay merit, JJ2's online multiplayer component remains one of my favorite gaming experiences. It strikes a near-perfect balance between mechanical skill with tight movement, tile-perfect trickshots, and a high speed ceiling, while most of the combat itself isn't based on mechanical skill but sheer tactical play. JJ2's gameplay is all about area control and denial, rather than straight up deathmatch. Things like hunters having a disadvantage due to running into enemy territory makes for tenser situations, and having a good read on your opponent's playstyle/priorities is a massive component of skill in the game.

Sure, this means that gameplay can slow down quite a bit when neither side wants to risk giving up control over territory, but this isn't any downside unique to JJ2, as it's present in almost any game regardless of its design philosophy. Non-duel games solve these issues by delegating roles to different players, and different roles have different priorities over which powerups to control or positioning to take. The inability to totally control your enemy's movement also means these roles need to change on the fly, which virtually necessitates players understanding how to be versatile and not rely on a single style constantly.

In addition, nearly nothing is designed to use randomness. Pickups and powerups spawn with clockwork precision, weapons use deterministic algorithms to determine their behavior, and the only two remotely random things I can think of mechanically are bouncers going through walls and walljumping. Neither is strictly random either, merely chaotic; the output is incredibly sensitive to the input and so can vary wildly with only a little change in the starting values. With near complete absence of randomness in the game, information and communication is the be-all end-all of competitive: knowing where you enemy last was and predicting his next actions, keeping track of respawn timers for every controllable resource on the map, keeping track of enemy's hearts and ammo supply as a form of risk assessment, and various other smaller tidbits.

As far as online multiplayer and competitive goes, the biggest dealbreaker has always been that JJ2 was never designed for it; it just happened to be a pretty good concept. Netcode is atrocious and incredibly unreliable, and the nature of the game means that having a very small player base keeps regional play from being feasible; virtually everyone plays on European servers, making it a very inconsistent and non-level playing field. Packets frequently go missing resulting in missing carrots or powerups for specific players, and constant desyncs of hearts and shots. JJ2's online component isn't a bad game, it's just a fundamentally broken one. Very little about it works, and that's the most infuriating thing about it.

As a concept and in practice JJ2's competitive gameplay is still my favorite of almost any game I've played, it just never friggin' works.

(so sue me I'm 2 months late to that discussion)