What that means is the bike's power is more than your average cyclist who can't put out 250 Watts for two hours like the ebike. That combined with the power from the human makes the ebikes, on average, likely to be twice as fast as a human powered bike.The power is 250W with a 600W max (I don’t know what that means, but others here do).
In your OP you make an ebike sound equivalent to a human powered bike. It's not. It's a different form of transport and should be treated as such.
I'm not worried about the conflict between ebikes and mountain bikes. It's the hikers and equestrians I'm concerned about. They already hate mountain bikers and have successfully limited mountain bikes from many trails around here. The conflict between trail users is already bad enough without adding another, faster, user type that will be lumped in with mountain bikers.
I'm fine with ebikes in bike lanes and bike paths where the 20 mph assist limit makes sense and bike commuting longer distances feasible. It's our heavily used MTB trails where I don't believe bikes like the one in the OP belong.
There is no reason they can't make an ebike where the total output (human and assist) is limited to 200 Watts and a max of say 10mph. I'd be fine with that on MTB trails, as it would truly be equivalent to a human powered bike.