[Maxatar]

I think I get the jist of your post and why IIA might seem objectionable, but your example does not reflect IIA and the claim that any voting system that satisfies IIA must rank Alice and Bob equally is not true.

The score voting system satisfies IIA and can result in a situation where 50% of votes assign their highest score to Alice and lowest score to Bob, and 50% of voters assign their highest score to Bob and their second highest score to Alice. Alice would end up winning the election and there is no opportunity for the introduction of a new candidate who could act as a spoiler for Alice.

Arrow's impossibility theorem does not apply to score voting since the theorem only applies to voting systems where you rank your choices, it does not apply to systems where you rate your choices.

https://en.wikipedia.org/wiki/Score_voting