If I use Migration Assistant to move my content from old Mac to new, will System content/ storage also be copied across?

I currently have an early 2015 Macbook Pro & am planning to buy a new Macbook Air because my keyboard & tracker pad no longer work. I've spent a good few hours going through my current Pro getting rid of old documents, clutter & photos don't need because good opportunity to tidy up before getting new laptop. While looking at the storage of my Pro I noticed that my System storage is very high ( ~117 GB). I've followed guides to manually clear logs & caches (& ensuring empty trash after) but doesn't seem to do much. Many of the system cleaner apps appear to require payment to actually do anything but there isn't much point if system storage isn't actually copied over– and considering that manual clearing did little, I wonder if there's a different problem going on? Alternatively I'm not sure whether it might be better to do a clean installation and manually copy over what I need to, but not sure how easy it could be to miss things?