I have a leaf (Nissan).
I’m not sure how the other mode (D) uses regen braking. I would assume very little until you press the brake, because it does coast. My normal mode is B, and regen kicks in as soon as the accelerator is released (which can actually be a little jarring/jolting depending on speed, so I first reduce pressure on the accelerator rather than just taking my foot off it like I would to coast).
I drive my car in town, and (pre-pandemic) on the freeway to work and back. Since I mostly carpooled, and also because my state allows single occupancy EVs to use the HOV lane, my driving on the freeway was 85% in the HOV lane (the lane ends about 3 miles ahead of my exit, otherwise it would be more).
Because yay HOV, I didn’t do a ton of crawling along at 5 mph, except when something jams up the HOV lane along with the rest of the suckers (yes, this is exactly how I think of them, my brain is not kind) in the normal lanes. B mode works great for this too, but is where I am more worried about getting rear ended due to lack of brake lights during one-pedal driving. I have to be paying attention to people jumping into the HOV lane from the normal lanes, and be able to quickly slow down. I can slow down more smoothly without jolting by just reducing pressure on the accelerator. It is rare I need to use my brake, but if there is a car riding my tail, I will generally drive slower anyways because I want more time to react to people in front of me (hopefully giving the idiot behind me also more time to react).
Regarding the acceleration down steep hills, I only have one somewhat near me (it’s an up/down overpass across some railroad tracks and another intersection), and it’s in a direction I don’t generally drive, so I’ll have to pay attention the next time I go that way. I do know in the Prius, when heading to my mom’s house which is “up the mountain” but has a lot of up & down on the way there, I will either put on cruise control to control my acceleration down the steepest parts, or put on the engine brake. I don’t like feeling out of control, and I don’t like riding my brake, so I let the car do the work (although according to Google, Toyota doesn’t use a CVT, it uses a “Power Split Device”).