They have had these rules in place for some time.
Yes - they can be sneaky - but it’s also well documented.
If you’re playing at that level and scalping bonuses - you need to be aware of what you are doing.
Sucks for the player - but this one is clearly not on the book. Arguing it’s “industry standard” is pointless - they make the rules - you accept by depositing or decline by not.
Situation can easily be avoided as a true arbitrage player by playing for cash and declining a bonus at a book who accepts higher limits. It’s not a straight arbitrage - it’s a bonus scalp in this situation.