I've found the exact opposite of most of that to be true. Maybe I'm just using different tires? What bike and tires did you have? I will say the $10 (if that) tires that came on my wife's fatbike performed about like that...but I wouldn't expect a $10 MTB tire to perform well on a MTB either. Of course the OP isn't looking for challenging trail rides so it's moot to him.
To the OP: Were the fat bikes you tried hub drive? If so, keep in mind a mid-drive of the same power will perform much better on hills. I do agree with some here that you generally don't need a ton of power to do well on hills with a mid-drive, but "well" on a trail ride where lower speeds are acceptable and you're in it for "the experience" is different than what you're looking for. You're trying to get somewhere in a reasonable amount of time without having to do interval training at the same time. So I think you are on the right track looking for something with lots of power. To add a couple more to your possibilities that haven't been mentioned yet to your list:
shop.sondors.com
Not really high-end, but the cheaper bits can be upgraded. The LX might suit you well. They use the Bafang Ultra.
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eunorau-ebike.com
Again, not super high-end but may get the job done for you. Quite a selection, some you may like use the BBSHD others use the Ultra either of which I think would be powerful enough to make you happy.