Actually it's difficult to exploit the HPS:

• First you need more stake than what is voting for the return proposal.
• Then you need to have more stake than what is voting on the other proposals.

Since only 1% of the budget is available for distribution an attacker would need to sustain this for a prolonged period of time. In the meantime the stakehlders can rally toghether and respond by:

• Voting on other proposals.
• Voting on the return proposal.
• The accounts attacking could be forked out or the governance related transactions can be blocked with a softfork.

Given the small payout relative to the amount of resources needed to carry out the attack it doesn't seem to be worth it.

The only way that you can sucessfully exploit the HPS is to have the majority of the whales coluding which is a hard thing to do. Even then dolphins and orcas have enough stake to counter the whales.

Right now you could maybe sneak in a proposal that doesn't benefit the network by being deceptive since the majority of the stake is not voting on proposals. By deceptive I mean to pretend to work on something that benefits the chain or by overpricing the proposal (remember the witness that had a proposal that was voted out from the HPS?).