If customs were made legal my complaint Would be that most likely the variations people use would always be made up of the best moves and there would be little incentive to pick others
You aren't wrong, but this will always happen when any kind of choice is involved. It's like saying NRS shouldn't bother adding new characters since KL will still be filled with Kangs.
The issue is that the devs are using the limited ability slots as a shortcut to balancing the variations and abilities instead of taking the time to address the bad or unbalanced abilities themselves.
I not very familiar with Skarlet, but if Bloodport would really he as common as you say it ge erally means one of a few things:
- The character is broken/fundamentally flawed without it and needs it to function.
- The other options are too weak and require changes to be viable alternatives.
- Bloodport is too strong compared to the other options and needs to be toned down.
You could of course split it up from the other stuff via variations like NRS is doing, but that doesn't really fix any of the potientual issues it just puts then in a neat box to the side where they hope the problem will go away.