The defence myth(nothing holds)

Stars already matters but for attacker more than the other. I would never run an attacker at 4* in arena like Fulcrum for example. I think it doesn't matter if a support or a tank is less starred than another one. The difference for tanks will be that they'll have less health and armour, but it can be compensated by protection and defense mods.
Since they introduced modules, stars are less important except for attackers. All is now matter of mods in the biggest part and gears..