I've not used TV built-in speakers for nearly 20 years but there is no doubt they aren't as good as even half decent hifi speakers. I find dialogue on Freeview clear. However, some movies (DVD) I find it harder, usually American. It might just be a language thing but sometimes I just don't hear what they are saying.

Chris
Srces: Squeezebox Touch | OSMC Vero 4K+
Procs: HD621 > G61R > Minidsp DDRC-88D
Spkrs: 7200.2 + 5KC + 5Ks | iNuke6K > USC15 | iNuke3K > 2 x Crowson T108SS
Video: JVC HD950 & 1.9m React3 2.4:1 screen
Room: 5.8x2.8m | Various GIK Panels