Overall it's questionable on muscle efficiency. The main problem with scooters/skateboards is that beginners don't learn using second leg (it feels unnatural and takes practice). Thus getting tired with pushing with one leg.
Another thing at this form factor you can get electric skateboard, muscles are concern.
Muscle usage between a bike and a scooter isn’t even close. The leg you’re pushing with isn’t the problem, it’s that you’re supporting your whole body weight on one bent leg while you’re pushing, and effectively doing a one legged half-squat every time you transition from coasting to pushing and back. Add in the additional rolling resistance from the tiny wheels and the lack of mechanical advantage from gearing and overall you have something that’s only modestly better than jogging except when you’re costing down hill.
My experience is only with using skateboards for long distance, though similar should apply for scooters, but haven't tried.
If I haven't rode both bicycle and skateboards for distance for a while, I'd have exact same thought as you. From my experience of casual rider, it's opposite - I can easily go for hours on skateboard, while on bicycle I get tired and uncomfortable. I've ridden same bike paths 10-20 miles on bicycle and skateboard, and for me skateboard is easier. My guess because on skateboard I can change body position and muscles involved, can switch legs, push or pump. While on bicycle I'm locked in the same position, using same muscles all the time.
Jogging is way way harder than skate, I can barely jog 5 miles, but on skateboard 5 miles i won't even sweat.
Another thing at this form factor you can get electric skateboard, muscles are concern.