There is something interesting to talk about here.
Because in dance music where uk mcs or toasters shine, theres less room for vocals and lyricism, so the mcs end up having to do his own bit of just 'hype' next to the hype the dance beat brings. I would argue uk mcs are more like instruments interpreting the vibe and reacting moreso than just interacting with a beat.
If you look at any trap track today you will find that the adlibs have a huge part to play. Not only in a musical sense where the beats break down to leave room for them, but also in the sense of the 'writing'/putting the words down and showing persona.
So my guess is most us mcs wont be able to do their thing with tracks that are busy in the way grime or jungle tracks are busy.
But then again the new stuff is shaped way more producers than ever before, so if they decide to make more demanding beats then fine.
There was a reason Magoo and Missy and similar mcs worked on timbaland beats, whereas he almost always had to make simpler beats for mainstream rappers.
Generally tho, mcs that get beats from drum machines (like most of the south historically) will usually be more apt at this sort of stuff because they end up mimicking or playing into more complex drum patterns than the older breakbeat beats from like golden era new york stuff would have you do..