What that tells me is that you're doing regular content and not putting a tank on your team. Yuuka you get from the start and Tsubaki is all but guaranteed given she's 2*, in regular content for every team you always want a tank and 3 DPS, a healer and the last one can be whatever you want. A tank is obviously always going to be a striker, for the other ones you can have them be a mix of strikers and specials, for example Kokona is a striker but she's a low cost healer so you could put another DPS or buffer into the special slot instead. Early on you needn't match the tank's damage type with enemy armor type as their damage fucking sucks anyway, at least that's the case for most tanks, all the damage should be done with everyone else so always match your damage dealers' color with the enemy's armor.
There are tanks that are better, or more useful in regular content, than Yuuka and Tsubaki but they're usually 3*, for example Tsurugi tanks, does big damage (especially when you use your EX that turns her normal attacks into AoEs) and is completely self-sustaining because she heals herself and can replenish her ammo after killing an enemy, but that also makes her completly unsuitable for bosses or raids since she obviously can't use half her kit anymore (exception is Chesed as it's a raid boss that summons tons of mobs). She can be useful in PvP believe it or not but it requires a very specific setup and PvP fucking sucks anyway.
