If one gains 51% of the network compute resources can he force drain the biggest wallet? How could he do it if he can keep that 51% advantage?
Mostly no, but also kind of yes. Obtaining 51% of the hashpower allows you to reorg the chain, meaning you can reverse transactions. The main way that 51% attacks can be used to steal is by double spending, e.g. buying something from someone using tokens, then reverting the transaction by mining a new block at that height.
The party doing the 51% can revert old transactions, so they could revert transactions that fund those "biggest wallets" you refer to, but they can't arbitrarily send funds from anyone to themselves.