There's nothing wrong with roaming as a support. It's a conscious effort to help another lane snowball or comeback without sacrificing much from your own lane by capitalizing on opportunities (the same a jungler would look for after they finish a camp).
If you die in lane while your support roamed, then chances are you overextended knowing that they weren't near. That's on you. If they left lane for 2-3 minutes at a time in laning phase and you get starved, then that's on them. But you shouldn't downplay a legitimate strategy just because it was done poorly. Do you know how many kills I get from 1v2 lanes just by playing passive and letting them get cocky and/or desperate because their team is pressuring them to try and force something in response to my support roaming? Tons. It works even better in Solo Q than in Ranked 5s because the enemy team is less prone to have good communication. So unlike Ranked 5s where they're warning each other about roams, you can usually get there when they're just realizing it because bot lane is focused only on winning bot lane (Welcome to tunnel vision).
Had Thresh played better on opportunities to get his mid lane ahead, and the enemy ADC played like he should've knowing his support was out of lane, then you would've lost that matchup overall because you can't force a kill on someone that doesn't allow you the opportunity. And you can't force a tower over an ADC early game unless they're really low. You could freeze the wave, but it'll push to them eventually and by then you're at a disadvantage via wave location.
You even said it yourself, roaming without a plan. That's not the same as a planned roam with a clear goal in mind. And the fact that you openly called them worthless is a pretty solid indicator that you can't even acknowledge how much your support is for you early game as an ADC, meaning you won't get very far in Ranked.
