Short answer - avoid the old bosch. Long answer:
You can get a feel for the resistance from the motor by turning the cranks by hand - ideally with chain removed , but if that's not possible have someone lift the rear wheel.
It's probably my imagination, but the old bosch and shimano motors felt like about as much resistance as a rusty chain, the yamaha feels like cheap pedals, and the brose ( specialized) felt like good pedals which need lubrucating.
Unless you're the type of owner who carefully applies ceramic chain lube every Morning and upgrades the bearings in pedals, you are unlikely to notice motor drag on anything except the old bosch.
IMHO , the real difference comes from the inefficiencies we accept in our e bikes but would NOT accept if we didn't have a motor.
Those fat and grippy tyres suck energy - plus I run lower pressures for comfort / grip because, well, I can just wind up the assistance.
The set up is different - over the 3 years I've owned my emtb, the ride position has crept more upright for comfort and I'm running the suspension softer . Every time I jump from my emtb to the kids regular bikes I'm reminded of how aggressive their riding position is and how light they are ( 45% extra weight for my ebike - sounds a lot more than 8 kg, doesn't it?) .
So I have customised the power levels on my bike to compensate - eco is set to 50% assist, it feels almost as difficult to pedal as the most efficient kids bike I own ( a VERY nice bike set up so she can keep up with me uphill) .
For perspective, riding at 50% assist with the tyres firmly inflated, I can easy get 80 km range on rail trail type rides - for an estimate of how much energy I am losing to the motor drag / tyre choice ergos.