How is Cap playable?

I've been playing Cap in Diamond, and although I get the playstyle, his kit itself just seems so bad. The two main reasons I'd say are his damage and his shield.

Cap does very low damage. People call Panther the tickle monster only because Cap isn't a monster. Against good players, they'll pretty much just ignore me as I struggle to do chip damage to their health bars. Supports just pretend like I'm an annoying fly that requires them to heal each other every once in a while—not enough to very meaningfully stop them from doing their normal role.

Also, I think he's got the lowest melee range of all tanks? Until you get the throwing discs, people can just outpace or juke you like crazy.

His shield also feels awful to use. Why the hell is there a COOLDOWN before you can put up your shield again, even when it's intact? Legitimately gotten me killed so many times. How am I supposed to block CCs when I have to wait to put up my shield again? Mantis/Luna literally just wait for me to drop my shield to stun me.

Not being able to shield in midair sucks too.

I've heard (including from a t500 cap), and also noticed, there's a bug where projectiles will sometimes go through your shield when you're backing up, which is total bs, too.

Lastly, the fact that deflected projectiles go in a random direction is just baffling. It takes away a possible avenue of skill expression and forces you to be practically point blank to hit anyone with a deflect.

I get it, Cap can be a pest and I'm usually good about not dying, but in higher ranks it really feels like I'm not being useful. Especially against a Rocket/Jeff, since I pose zero threat to those supports, as well as some dps that can actually just melt me, shield or not. Not to mention the infinite CC options that can ruin my escape. All so I can run in and slap them with a wet fish.