And just for the sake of argument, depending on how you did your research, would getting a more expensive amp and a less expensive cab give you a better sound then an equally priced combo.
(note: the above example was not meant to compare brand names or anything of the like, but merely to express the above question: Would x amp and y cab sound as good/better/worse than y combo?)
No better or worse sound. Different. Sealed cabinet vs. open back combo...whatever.
Of course, a cheap cabinet will undoubtedly SOUND like a cheap cabinet.
So it depends entirely on what you wish to accomplish.
Do you WANT to haul around TWO pieces of equipment instead on one? Get the head and cab.
I took this Fender amp head...
...and put it in a 1-15" combo-style cabinet.
Does it SOUND different?
Well...yeah. But only because it's in a completely different speaker environment and configuration.
Like comparing a Gibson semi-hollow 335-style guitar to a Gibson solid body Les Paul guitar. Same pickups, tuners, knobs, bridge, stop tailpiece, etc....yet a completely different vibe and physical sound.