The issues you address, as well as many other issues with the voting system, can be addressed easily by changing one number in the code: the voting delay.
By introducing the preparation period with it, all the attacks become harder to execute, as it gives time for UNI holders to mobilize their voting power.
And the outcome of the attacks and the cost of them become much less predictable for attackers.
When it comes to lending platforms, mobilizing UNI means that lenders have to pay bigger interest.
In any case, as long as there’s time to respond for the Uniswap community, I don’t think these attacks would happen in the first place.
The only way you can make a malicious proposal to work while bypassing the governance procedures - is if you have the ‘effective’ majority of the voting power.
If you do have it though, it doesn’t make sense for your direct financial interests to make such a proposal go through.