Round trips for parallel requests work fine over HTTP/2. (As long as there aren't vast numbers of tiny requests, for example every cell in a spreadsheet).
However, sequentially-dependent requests are about as slow with HTTP/2 as HTTP/1.1. For example, if your client side, after loading the page, requests data to fill a form component, and then that data indicates a map location, so your client side requests a map image with pins, and then the pin data has a link to site-of-interest bubble content, and you will be automatically expanding the nearest one, so your client side requests requests the bubble content, and the bubble data has a link to an image, so the client requests the image...
Then over HTTP/2 you can either have 1 x round trip time (server knows the request hierarchy all the way up to the page it sends with SSR) or 5 x round trip time (client side only).
When round trip times are on the order of 1 second or more (as they often are for me on mobile), >1s versus >5s is a very noticable difference in user experience.
With lower latency links of 100ms per RTT, the UX difference between 100ms and 500ms is not a problem but it does feel different. If you're on <10ms RTT, then 5 sequential round trips are hardly noticable, thought it depends more on client-side processing time affecting back-to-back delays.
