Going between Android and iOS, that's one of the hardest aspects that I think gets overlooked - the browser is just slower and its noticeable. I pointed out the flagship device in this case, but its no better on the lower end devices.
You can see in this video: https://m.youtube.com/watch?v=83dDLf3Zhx4
It’s interesting to note the different behavior; Android/chrome is putting something on the screen first, while safari tends to finish rendering and show the completed result before chrome. Tends to vary a bit by site.
App startup is a bit slower on iPhone but note that the preferred way on iOS is to keep apps open and not manually close them. Manually closing apps isn’t really required on iOS except to declutter the task switcher. Supposedly faster startup times coming in iOS 13.