When costumes were released for S1 heroes, they were ostensibly to help S1 heroes be competitive with newer, stronger heroes.
Now that costumes have been released for the remaining S1 heroes, it looks like costumes for the likes of already strong heroes like Finley and Killhare are looming on the horizon. These heroes are already very powerful. In fact, they were the very heroes that necessitated the buff to S1 heroes in the first place. They have no need for buffs and yet, that is exactly what is going through beta now.
For the sake of balance, these heroes should not get any costumes.
Instead, if a hero is found to be sub par, they should be buffed directly (with either stat changes or tweaks to their skill or both). However, for special heroes (i.e. non S1 heroes who could only be summoned by spending) it is unacceptable for these buffs to be blocked behind yet another RNG paywall (like having to summon the same hero again).
Heroes like Perseus and Inari who are weaker than many contemporary heroes could use these buffs. Heroes like Finley and Killhare who are already at head of the pack, do not need them.