A lot comes down to intended use.
On my 55x, I only use it (and also my STX 65/95) for confirmations and not for glassing. So any "narrow view" issues (real or perceived) are immaterial for me. However, it someone uses their spotting scope for glassing it could be an issue; reality is it won't take that much longer glass a hill side.
My personal experience on eye fatigue: it is clarity that determines how long I stay in the glass rather than anything else. I can put my old 8x Viper HDs on a tripod and glass. But it sucks and I won't glass long. However, I can do my SLC 10s or 15s and see no noticeable difference in glass time. I don't glass with my spotters (STX 65/95, Kowa 554) but I never have pulled my head away due to headaches, fatigue, etc.
As far as 77x vs 88x, we tend to over-fixate on weight and not volume. The item below is from the Rokslide review on the 99x. While the weight in higher, the total volume (think pack space) is not that much more when looking at the 88x vs the 77x. You also have to remember that Rokslide members get awfully frugal on their optics and do make compromises (unlike the multiple custom rifles and gold-plated scopes in their safes). For a chunk of last year it was nothing to get the 88x for a couple of hundred more than the 77x with just a bit of leg work.
Here you can see the TSN-99 (2nd from the right) next to a Swarovski ATX-95 on the right, and TSN’s 88, 77, and 55 on the left in descending order.