As a teenager a friend found some antique swept back motorcycle handlebars that had the same expansion nut type fitting as my bike and we had to try them out; the handles just touched the front of the saddle when turning very sharply - with any kind of speed, not at all. The point is the amount of force that could be applied to the pedals was greater, because pulling up on the handles was close to being in line with the force down. As analogy, it was like lifting a weight in a straight line from standing above position instead of having it out at arms length and trying to lift. My father immediately ordered their removal as unsafe - it certainly made it (too) easy to wheelstand both from centre of mass being further back (upright position) and that greater force. However, if a bike were designed to achieve that in line pull on handlebar/push on pedals, would performance, especially uphill/against the wind be improved? I think recumbent designs may use this effect.
For one thing, the aerodynamics are terrible. For another, most cycling is not dependent on peak power, but on sustainable power, for which leg strength (or body strength) isn’t as important as cardiovascular capacity.
Some recumbents do use bars like the ones you mention, but the geometry is so different that muscle recruitment is also very different.
Many cruisers have swept-back bars, as do some bikes designed for more athletic riding (notably Jones Bikes).
I have two bikes set up with Jones bars (one an aggressive hardtail mountain bike, and one a cargo bike). In line with your experience, I’ve found that muscle recruitment and force alignment are affected by having a vertical line through the grip and the handle bar, and I can apply significant downward pedal force. In conjunction with wide tires, I've found that this allows for an interesting ``hiking" motion over roots and rocks.
In places where wind resistance is a factor, the upright position does amplify this. (Jones' design compensates for this by offering alternative grips in a more forward position).
In addition to aerodynamics, there are two more things:
- It is more efficient use of your muscles to pedal faster in lower gear, except maybe for very short bursts
- Clipless pedals or toe clips and straps also allow one to push pedals harder than one's weight, but don't have the problem with aerodynamics or require arm strength.
What you've done there is reinvented what's called a "sit up and beg" bike. Upright position with swept back bars. It's an old school upright bike of the sort your grandparents might have ridden, along with anyone Dutch.
Why they're not so common any more is primarily a matter of fashion, replaced initially by mountain bikes (cooler) and then by hybrids (mountain bikes with road gears and tyres), though I've noticed the hybrids of recent years increasingly moving back towards those swept back bars.
Don't get the idea they're in any competition with drop bars and road bikes. For getting around town at low speeds the upright position gives you much better all round visibility and easy pedaling.