Also, I don't trust Apple 'future proofing' anything. In 2006 you could've had G4 Mac Pro with 16GB for future proofing but in 2011 it was useless.
We're not talking about
maxing something out with 16x it's base spec to "future proof" it in the hope it will magically last a decade - we're talking about starting out with what is
already the base spec (16GB) for competing machines so it doesn't start running out of RAM - or wearing out the SSD - in the next year or so.
Assuming you mean the 2006 Intel Mac Pro (no such thing as a "2006 G4 Mac Pro") - that machine came with 1GB. "Future proofing" would have been upgrading it to 2GB, not 16GB, which was pretty extreme in 2006. Anyway, that sort of "future proofing" was unnecessary because the RAM then was user-upgradeable. The only reason for maxing it out with 16GB would be if you really, really needed - right then - 16 times more memory than the base spec.
I actually had one - and because 1GB was very limiting, later upgraded it to 3GB with a 3rd party kit (ridiculously easy - didn't even need a screwdriver; still cost £200 but that was a lot less than Apple wanted) - and it was my main machine until 2011 - and the only reason I stopped using it then was because I needed to switch to a laptop, it was still quite usable (and could still have been upgraded if I'd wanted). If it had been stuck with the original 1GB RAM it would have been landfill by 2010.
Likewise, the next system was a 2011 MacBook Pro - bought with 4GB RAM - lasted me till 2017 but only because of a mid-life upgrade to 8GB and a 256GB SSD. 2017 iMac - ditto, standard 8GB
ridiculous for a high-end i7 model, but adding a 3rd party upgrade to 24GB was a cinch.
There's a pattern here - many Macs come with a paltry amount of standard RAM and have done since forever, and Apple charge a ridiculous markup for upgrades. That used to be mitigated by the fact that most Macs were upgradeable with cheap (but often the same parts that Apple sold) 3rd party products, That's no longer possible with Apple Silicon, yet Apple froze their base RAM specs
and upgrade prices sometime in the mid 2010s - even with RAM prices falling and RAM
demand increasing (a 4k video, or "retina" image occupies 4x the space of standard def... )