I think bicyles will become a primary transport in the next decades, electric or not
And yet I own an electric bike, and love the thing. Because I can go up that hill in my work clothes, and not show up a dripping, sweating, stinking mess. I can go down the hill from the house and get supper without having to don the clown outfit and the special shoes. Just wheel the bike out the garage and go with whatever I have on. Back up the hill to get home, give that electric motor an extra kick if I'm feeling lazy, sorted. And that's for an old ex-racer who is in probably better shape than 90% of his peers. Imagine the worlds that open for the elderly, overweight, or other "differently abled".
Bicycles have had over 100 years to "become primary transport" and unless one lives in the Netherlands, it obviously isn't going to happen. Stick a battery and electric motor on one, though, and suddenly one's practical range and power band is extended enough to make it a viable transportation alternative for not just the fully-abled and in-shape, but for nearly everyone.
Instead I'll just point out that being young(ish), (reasonably) healthy, and having only slightly uphill to worry about, are all luxuries.
Electric bikes make bicycling accessible to many more people, and their embodied and operating energies are quite modest.
Best of all, they don't take away your ability to ride a pushbike! Or brag about it on the Internet.
According to my logs, I go about the same speed and heart rate on my cargo e-bike with my son and our gear commuting. The difference is that it saves enough time and helps with one notorious hill enough that I do it every day year round except for the worst weather whereas before I used to skip a few days a week — and I say that as a fairly fit cyclist who has ridden centuries at gun-timed speeds in the low 20s, so we're leaving out a LOT of bike commuters if we're saying that's inadequate.
I see e-bikes as a transformative technology for cities. If we want to stop the death, pollution, and quality-of-life impact of cars we should be rolling out bike infrastructure as quickly as possible — it's the cheapest, most flexible option we have. (Buses are second: more accessible, all-weather capable, but less flexible)
Since we got ebikes, we've averaged 2,000-2,500 miles per year on bike and sometimes go a couple months without using our car, which we are likely not going to replace when it dies.
It allows bikes to be a substitute for far more things that you'd otherwise use a different mode of transportation for.
However, I can haul over 100lbs of cargo and/or kids on the back of my e-bike, and can show up to work ready to go. Given that the ride to work includes climbs, and I would need to shower, the e-bike gets me there substantially faster. If I need to pick up a kid from an afternoon activity that is downtown, I can do so on my e-bike (I live about 13km from downtown, which my teenagers can do, but is a rather long ride for my younger kids to do).