How do I deal with my team being a handicap?

If your team is a handicap, tanks/supporst are the most team reliant roles there are. I would not advise them. It's so much harder to carry from a tank or support (ignoring like brand/zyra/velkoz/xerath)

carry supports are probably the best way to go man (the brands, zyras, etc) because you control vision, damage, peeling, and sometimes healing (sona) so many different things are at your disposal, granted you don't do the max amount of damage you can still have a significant impact on the game.