Do you need all those muscle groups though? People have experimented with bikes that added arm cranks to the regular leg cranks but basically found that your legs are more than able to drain the tank of whatever actual power you have available. It may be that the big muscles at the tops of your legs are also able to do this on their own.

I agree that Moisture's sensation of a heavy upper body may be to do with weak "core" muscles in some way. Interesting that it's on one side as well.

Another weird feature of old Dutch bikes that I think Moisture might be trying to recreate by putting his seat as far back as possible is the super slack seat angle. This means you can't put your weight into the pedals. But you can pull back on the handlebar and push forwards almost as if riding a recumbent. This would actually use some arm muscles-- you could almost row the bicycle like a boat!

We talk about these bike designs like they're for popping down to the shops on. But back in the days before cars were affordable people used to ride enormous distances and this was the design they came up with. It's hard to compare because anything radically different from what you're used to feels weird.