If it's any reassurance - I was charging my mg5 lr at a gridserve 350kw charger the other day and there was a e-Niro (71 plate so not the Niro EV) charging at the same time as me. We both had about the same level of charge at the start - I peaked at 90kw, his peaked at 73. Mine throttled slowly down to 57 as it neared and passed 70% charge, and his rate was consistently 15-20kw below mine. I'm far from knowledgeable, being new to EVs, and maybe my battery was warmer but it seemed like a fair comparison.
I can't see the MG4 having a worse charging speed than the 5. If it equals or exceeds the 5 then you should be ok.
If I am talking out of my backside and being an idiot, I'm sure someone will be along to tell me shortly
Edited to say I had scanned your post and missed the line about quality 150kw chargers. The 350 chargers are the only rapids I've tried.