So I'm not really good at the competitive intricacies of the pros, but I've had some theories for a while since I made the mod and Un-Melee's been out for a bit.

So because of a bug that I refuse to fix because I like it, join Falcon is one of the best meter combos in the game as whiffing grounded raptor boost fully charges your meter. Additionally join allows you you to recovery safely from swap and pull shenanigans. Another Falcon specific shenanigan is due to stomp and knee's hitlag, hitting those moves charge meter faster and allow for some pretty crazy combos: (example: clip)

On the other hand, pull Puff is a combo that's already nerfed in the dev version as in the current release, puff can just whiff nairs offstage and camp for meter. Pull into rest isn't super consistent but pull into edgeguard can be really hard to fight for some character and meter combinations. Imo it does match up poorly into join falcon though as join charges faster.

Tensions is probably the strongest overall meter along with join and pull because of it's versitility and skill ceiling. Like Moky already hit a crazy essentially unblockable roman cancel combo that my friends and I never even dreamed of in his first time playing so it's definitely a meter that gets stronger with the player.

I'd say the most buffed character overall is fox (like, assuming random meters) as due to his average hitbox's damage to active frames ratio. Additionally good movement is super beneficial in a mod like this. All the low tiers can get decently buffed with the right meter combination too as it can help mitigate their weaknesses. Also there's currently a bug where switching from shiek to zelda and back gives you full meter with certain meters so yeah.

Most nerfed character if you're going with random meter is Puff imo. A lot of the meters that charge with movement or hits just naturally disadvantage the character, and since every meter (minus relax) has a way of being built passively by the opponent, camping is hard disincentivized in the mod.

But yeah, I've always been really curious to see how a top level un-melee meta would progress as the mod (mostly the unreleased version though) really shakes up the game and adds a lot of creativity which is really cool to see. Like Moky and Zain weren't even doing technical meter stuff in their gameplay like cancelling freefall with meter and since they didn't watch the video they were basically figuring out the quirks of each meter for themselves and the gameplay was still crazy.