On the battery level topic: I honestly recommend just using Battery Voltage instead of Percent. It's a more honest reading, will take you a bit to get used to it, but it's a proper look at charge level. You can swap between either option right inside the display settings, typically.
As for the assist difference between mid-drive and hub motor: Biggest difference is that a hub motor has to output power over the full range of rear-wheel RPM, 1:1 relationship, and this is why hub motors are only really efficient when their winding, RPM/V, wheel/tire size and average riding speed are all in their respective sweetspot in relation to each other. Peak speed is quite easy to calculate, and at what loss of efficiency, the same applies to low speed inefficiency with hubs. Geared hubs introduce a fixed reduction ratio, but otherwise mostly follow the same rules.
With mid-drives, you can alter the equation through chainring and cassette sprocket selection, and with the Bafang Ultra, it's a very easy equation to figure out, since the Ultra is designed for it's peak efficiency output at normal rider cadence. This corresponds to about 60 RPM (1 revolution per second) at the bottom bracket. At this output speed, or anything up to 100+ rpm, the Ultra motor is very happy and efficient, and so is the rider... It was designed to be this way, and it tells you a lot about the great engineering team that conceived this motor.
Thus, to get your preferred riding speeds, you need only pick the right chainring and cassette range to get what you want out of the bike. If you're a street demon who likes to match speed with city traffic, a big chainring and tall cassette are nice... For most riding, a middle/upper sized chainring with the stock cassette range does great. For more trail/climb oriented riding, a medium/smaller chainring works wonders. It's worth noting for any calculation, you will never have smaller than an 11 tooth "high" sprocket, this is the smallest possible cassette sprocket on a Hyperglide (HG) Hub Spline, the stock format (and best format for ebikes).