That isn’t how physics works - you have to spend energy to counteract that kinetic energy you’ve ineluctably released by going downhill.
This sort of edge case maximalism feels useless and needlessly contrarian - it seems as though if I were to claim you can pay for things by credit card, you’d claim “that doesn’t work what if the power is out”.
What are you on about? I do hilly rides all the time and personally feel the pain of not being able to reap the benefits of the climb _all the time_. Let's say I climb a big hill and there's a red light at the bottom of the other side. Guess where all my precious kinetic energy goes? It dissipates as sound and heat into my brake pads. Whoops! I ride about 60 miles a week on very hilly terrain. Off the top of my head, I can think of 3 very large hills that end in a stop sign at the bottom in the first 20 minutes of my regular ride! I actually can't think of a single hill where I'm totally free and clear going down the other side.
In my experience, hilly rides are just harder and I'm more tired after them. It's actually very surprising that what I would expect to be a common sense viewpoint is being considered the contrarian one! Sure, apply elementary physics and hills are meaningless, but apply real-world physics and maybe they aren't so meaningless. And we aren't even considering the differences in energy efficiency when your body has to work harder, or the major differences in energy loss through air drag at high speeds. There are also concerns about how comfortably and efficiently you are able to convert muscle energy into motion through pedaling (similar to how speed-walking gaits are very inefficient) at both the high (downhill) and low ends (uphill) of pedal RPM.
This sort of edge case maximalism feels useless and needlessly contrarian - it seems as though if I were to claim you can pay for things by credit card, you’d claim “that doesn’t work what if the power is out”.