Balance is actually a priority. Thanks to the Aleister and Invocation limits, hardcore F2P farmers can't abuse those cards against other F2P who have less gems.
The game became more balanced amongst players who only use gems.
Aleister caused like 5 limits or more, spectralsword caused 5, citree caused 4, brave neos caused a bunch, d. draw and onomatoplay also contributing a lot, an there still more problematic cards to mention
If Konami's had banned/addressed the cards/skills that were the real problem the banlist would be like 1/4 of the size it's now
Just look at what they done to evil hero consistency skill, or gimmick puppet. If onomatoplay is very balanced, there is literally no reason to add some strict restriction to those skill either.