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”.
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 fast walking gaits are very inefficient) at both the high (downhill) and low ends (uphill) of pedal RPM.
The big hills I can think of near me all have either stop signs at the bottom, or another hill to climb.
Not really. Bikes don't have a battery to store reclaimed energy, if that would even be a thing. Maybe you go a bit faster on the downhill; I wouldn't call that reclaiming energy.
> Mass doesn't matter as much as people used to think.
On a flat road at a constant speed, mass doesn't matter (except for the slightly increased rolling resistance). With speed changes (in situations with sharp corners for example, or if you want to accelerate fast to escape from the bunch or to catch someone else) or in hilly/mountainous areas, mass does matter.
For recreational use, spending lots of money for shaving of a few grams here and there is not worth the effort, that's true. But a few kilograms more or less do make a difference.
> Hence no modern bikes being made out of drillium.
Modern top-of-the-line road bikes for climbing are already as light as allowed by the UCI. It makes no sense to drill holes in such a bike: you wouldn't be allowed to use it in a race.