The number of connections to one host isn't relevant in HTTP2. As ublock is blocking some ~20 connections these are going to different hosts. Connecting to a different host in HTTP2 is no different then HTTP1.1
If your HTTP2 is terminating at MANY boxes within your infrastructure you are failing to understand how HTTP2 works. Connections within a single TLS/TCP/IP connection are free, new TLS/TCP/IP connections cost exactly as much as before.