The only reason for people not to complain about the money-grabbing poor excuse for a new 'feature' is because they're idiots who only think 'oooh I can get more DPS!' and hide it behind a pathetic 'you deserve the money!' facade. Something like this is the lowest of the low and a good reason not to spend money on this anymore.
Doesn't need a buy all button at all, it would be a complete waste of UI space. The game should simply calculate the most efficient way to all current gold at the moment of a reset could have been spent and do the levelling for you. There is no use for a max all button except for resets, so adding it to any other part of the game would be completely worthless. And since nobody would say no to a question asking if the player wants all his gold used for levelling during a reset, it shouldn't be asked.
Our group has seen it all happen before. Not once, but hundreds of times. And we've grown through every single one of those times. But no matter how many times the world is reset and we become even better versions of ourselves, there is one flaw we have never been able to get rid of... No matter how many times we get betrayed, we are never ever able to think the best of all those people who broke our trust before as enemies and just keep helping them over and over again.