what my wonder was, is if it penalizes you for having a huge wallet staked, what would stop you from making dozens of wallets and staking them all with smaller increments ?
Nothing, and doing so would be a Good Thing (tm) for the network security, which is the whole point

The problem with "normal" PoS is that you have no incentive to do the above, under normal PoS, you get the same interest if you have all your coins in a single wallet and stake a few hours once a month, than if you have your coins spread over several wallets that stake 24/7.
However, if you stake once in a month with a big wallet, you run a high risk of forking the chain, while if you stake 24/7 over several wallet, you contribute to the chain stability and security.
Under PoS miners are stakers, but the chain is not absolved from the need to "mine" 24/7, which means enough wallets need to be staking with enough coins in them 24/7.
In terms of stability and security, a whale staking once in a month has the same effect for a "normal PoS" chain as a big multipool jumping in once in a month has on a PoW coin. Unless you want the network to be unstable and insecure, you want to discourage whales from staking once in a month, and encourage them to stake 24/7.
PoS does not just changes the inflation, it changes the responsibility for network security.