The main advantage of the photo browser over the explore-observations page is that it shows all the photos without needing extra clicks. But at genus and above, it doesn’t, which can be really annoying when you’re doing certain searches. E.g. https://www.inaturalist.org/taxa/324076-Criorhina/browse_photos?place_id=78388 , where there are only three observations, and the best photos are hidden. One issue here is that many species are difficult or impossible to ID to species, so a lot of very good photos won’t ever show up in the photo browser.
I suggest adding the rest of the photos after all the 1st photos, to avoid issues with observations with 20+ photos dominating a stretch of the page. This would also mean that the photo browser experience wouldn’t change until you reach what previously would have been the end of the page. Making the species-level pages behave the same way would be nice too, and probably simplify the code a bit by getting rid of a special case.