This is true. I used to have bad reception at my gym. Safari and Apple Music were so choppy on my 13 PM now they are smooth as butter on my 14PM.
In my house on T-Mobile with my 13 Pro Max I would get 150 - 200 Mbps download when on 5GUC. Now in the same locations with my 14 Pro Max I am seeing 500 - 800 Mbps. I can have both a 13 Pro and 14 Pro next to each other and the 14 is double the performance.
Something else has had to change other than just a modem to get double the performance.