In many-to-most cases 4G and especially 5G will simply outperform Starlink. If you have the 4G it may not even be necessary to bother with the Starlink. Unless you want redundancy of a 2nd connection or you can only get a really terrible data plan running both is not likely to make much sense. Starlink also has very onerous North-South field of view requirements that are actually often hard to meet even on completely remote sites (speaking as a Starlink customer with a handful of trees in the yard). Cellular is nowhere near as fussy about placement.

Starlink makes most sense when you have no 4G or 5G reception at all, generally speaking.