How http3 is reducing response time on slow connection?

HTTP/3 (Quic) is advertised as it reduces round trip time by using UDP instead of TCP. In theory, it reduces response time on slow connections (high latency). When I take a test on my computer, I see nearly no difference. Am I making a mistake or which tool to use to see a difference?

I have two servers in the same country which have roughly 50ms latency on a regular cable connection. I use Chrome / Dev Tools -> Network Throttling.

In theory, http3 should be faster on a 3G and Slow 4G connections but it is not.

Cable Connection: HTTP2: ~50ms HTTP3: ~50ms

Fast 3G: HTTP2: ~585ms HTTP3: ~565ms

4G Slow: HTTP2: ~155ms HTTP3: ~155ms

4G Regular: HTTP2: ~55ms HTTP3: ~55ms

This is a misunderstanding: QUIC does not reduce round trip time, it has shorter connection setup times because it doesn't have to do multiple roundtrips (as the combination of TPC + TLS does) to setup a connection.

Round trip time is a property of the network (or more precisely: from the network path) and is not any different for UDP or TCP (or any protocol used on top of IP).