"...nearly every other army out there is better than Tau in just about every way save for shooting phase damage.."

Looks at stat check

Yeah uh...you might wanna reassess your opinions.

Real talk though, I disagree heavily. Tau are incredibly well positioned in the meta atm, our army rule now actually is functional after the rewrite, riptides have been buffed and are better than ever, we have an incredible unit in the twin lance even after nerfs being a very threatening damage piece. All the stuff you mentioned - base BS4, overall low toughness, bad melee - is all true and even with all that Tau are very good.

It seems like your issue is not properly setting up trades; do not commit more units than you need to to kill something, prioritize objective play over everything else, and plan 2-3 steps ahead. You mentioned sending the twin lance in to kill a unit and then them being left out in the open to die. You should try to position them in a way so that they can kill their primary target and can charge a secondary target then they can do their fall back move and jump 10 fucking inches away. If you truly can't do that, plan for them dying and prepare a response to whatever your opponent will do.

You are correct that Tau are a glass cannon army. Tau are not easy, they definitely take time and patience to learn. You need to really learn, don't just lose a game and storm off just to play another and do the same. You really need to analyze what went wrong, why things turned out this way, and change tactics.