You are comparing desktops to phones.

I do most things on my desktop for the reasons you say but on a phone multiple tabs etc is a pain.

No, I’m saying that the booking.com app, or the Skyscanner app or any of their competitors don’t support multiple tabs.

Their websites do (although even on new phones you are at a greater risc of a tab being purged and needing a reload, but still you can multi tab on the mobile website)

Ah the difference here is that I can't use multiple tabs on my phone as they are too small. So tabs are only relevant to me on desktops and even then I will often use new windows.

I almost always book via apps. I can compare flights by looking at Kayak (app), then actually book it in the carrier app. I think the workflow just has to adapt to the tools you’re using, and trying to follow the same methods you’d use on desktop just don’t work. I don’t think either particular method is objectively worse than the other for every use case.