It does sound as if the bike behaviour is normal. On road I'm nearly always riding faster than the motor assistance, that's why I have leg muscles

. The motor is still helpful in an urban situation where you've a lot of stop and go. Off-road going uphill is when the motor really shines.
Yes it helps being in the right gear when the assistance cuts out. And mid-motor ebikes perfer higher cadence less force pedalling in general. The Bosch will (if you've a display like the Kiox 300) actually complain if you're pedalling in too high a gear for it's comfort. I had to adjust my pedalling style with the new bike.
Older motor models apparently had noticeable drag when riding over the assist speed, but that's not (or shouldn't be) a problem with the current models.
Note you can adjust to some extent the motor behaviour in the Flow App under customise riding modes. I bumped the settings up a bit for Turbo, emtb, and slightly for tour+ modes. You can't however increase to assistance to over 25kmh. Maybe still have a look though.