Direct Drive (DD) hubmotors have a bad reputation on hills from years ago when a lot of new ebikers bought a high-RPM cheap yescomusa hub kit, put it in a large diameter wheel, and fed it low watts to save the cost on the battery. The yescomusa has the cheaper/thicker laminations, so it is not as efficient (lots of battery watts converted to heat instead of power), and the power cables had to be thin enough to pass through the hollow axle.
The Yescomusa remains a useful option on flat land and 48V X 25A = 1200W. I have been dirt-poor in the past (however, no mullet), so I empathize with builders on a tight budget.
Our friend Luke/LFP is at the other far end of the spectrum. He is a fan of a very large DD hubmotor and using "too many" watts. The simplicity of the DD hub is at the core of its reliability, if...used within its limits.
The Crystalyte 35mm-wide stator series was the hot rod around here just a decade ago. Back then, it had the thicker 0.50mm laminations (less efficiency/more heat produced per applied watt), and the axles were adequate for the advertised 1500W, but...throw in 3000W and heavy regen? the axles broke. Plus, the thin motor phase wires got hot at 3000W. The newer Crystalytes are 'better', but...
If you want something a little lighter and a little cheaper, get the newest Crystalyte or the latest Leafbike 35mm motor. Nothing wrong with them. If you do get them, consider adding oil-cooling (find the ES thread, its worth it), or Ferro-Fluid.
The Edge has the thinner laminations (battery watts get converted into less heat), and thicker motor phase wires, and most importantly...the cast aluminum stator support that acts as a heat sponge. No moving parts, no leaks (like adding oil-cooling), and never needs to be topped-off once a year (like Ferro-Fluid, although...I did add FF to my Edge motor).
When you accelerate from a stop, there is a burst of amp-flow to get you going. Then...as you cruise along at 30-MPH+, the amp-draw goes down to the level that is just barely needed to maintain speed. Less than half of the peak amps drawn. Consider this...how much time are you accelerating? How much time are you in "cruise mode"? If you have enough motor and also enough battery...the acceleration phase lasts about four seconds (*insert smile here).
Then, you cruise along until you hit a red light...maybe a minute later? During those first four seconds, the motor is getting hot from high amps, and then?...during the following minute, it is slowly shedding it's heat to the outside air through its aluminum sideplates. That is not an ideal heat-flow path, but if you add the aluminum mass of the Edge stator support, some thermodynamic black-magic occurs.
I added FF..."just because". That being said...right now I "only" use 52V X 45A =2300W, and the damn thing doesn't even get warm. How much of that is the aluminum "heat sponge", and how much of it is the FF? I don't know.
Luke and "John in CR" have shown that...if you have a big enough motor (copper mass), and you apply enough watts (max volts + amps dependent on heat), a DD hub can conquer hills, and do it reliably. If the Edge 35mm wide stator gets hot on your hills running your watts, go to more watts, or upgrade to more copper mass by swapping to the MXUS 45mm wide stator motors.
If the MXUS 45mm motor is getting hot on your runs, upgrade to the QS 205 50H with the 50mm wide stator and deeper slots to allow more copper wire wraps.
Is 4000W the "true" limit of the Edge? That depends on the diameter of the wheel (smaller is better), and how often you actually apply 4000W (get a temp gauge, limit motor interior to 140F / 60C).