What makes you an expert on what makes a feature a gimmick? You have no idea of how other people use and optimize their productivity workflows around the use of this "gimmick". Your opinion is far from "objective" .
Split screen done well would be a killer feature for me. Last time I looked Edge support was ok, but not great. But what kills Edge for me as a daily driver is the basic usability in managing bookmarks and tabs. It's stop and go for every basic operation like dragging objects while Firefox is simply a continuous flow. Firefox is invisible, Edge just gets in the way all the time.
Otherwise Edge is not bad at all. Chrome without MV2 is dead to me.
People spend a lot of time in the web browser. So yes, they want to have a comfortable experience with it. And those features are deal breakers for a lot of people. So stating that they are not killing features is just unreasonable at best and ignorant at worst.
It does makes the difference to people who use browsers for something more than reading HN or Reddit. That's the point. What arguments do you expect? Specific use cases for every feature each browser has? That's a different discussion completely.
It is all a gimmick but as long as people are switching to a chromium based browser and not Firefox I'm happy. With that said, I don't know how anyone would trust a small team to build them a secure and safe browser. Chrome is so battle tested at this point and Google puts a lot of resources in maintaining it, they stand to lose a lot more given their scale.