To me it seems you are making things harder for yourself. You want it good for every situation, like you want 4" fat tires for offroad and want 2" tires for normal riding ALL ON THE SAME BIKE!Two controllers 1 for hills and 1 for top speed on flat.
If your doing it for a hobby or you are doing it to cheap out then your efforts makes sense. Otherwise I dont see the value.
You ever hear the term K.I.S.S. (Keep It Simple Stupid) Keeping it simple and stupid makes for a better experience. Start adding to many things into the mix and it can complicate things.
Yeah a $100 Unite motor is cheap, and its probably a brushed old technology motor, yet you link to brushless controller so I don't know and never paid much attention to the Unite motors such as you link to. They are cheap, but so are lead acid batteries yet ebikers dont use them, yeah some do but lithium is where its at. See what I mean old tech is lead acid battery, lower capacity (70% used ah rating due to devalue of lead acid) vs new tech is lithium, lighter, smaller, more capacity used.
There are two speed hub motors, maybe no big power as I see you link to a 3kw Unite motor. 2wd hub motor is about as complex as I would go, but one bigger power hub motor is not complicating things. Like going for a mxus 5000W hub motor instead of 2xLeaf 1500W hub motors.
(K)eep (I)t (S)imple and (S)tupid
or it might mean
Keep It Simple Stupid, but lets not call anyone stupid. Its just ebike fun