They really should put limits to cards like this that are horrendously overpowered and break the game completely. No reason why they should be allowed at full 3.
Depends what Hero variant you're talking about. Destiny Heroes for instance aren't tiered right now. Elemental Heroes on the other hand aren't tiered either. But Masked Heroes aren't tiered as well. Some other variants might be viable too but they aren't tiered at all.