I see what you're saying, but I think the mistake here is assuming that the Reserved List is the only way (or even the primary way) that Wizards respects the secondary market value of cards.

It's clear that Chronicles/4th Edition was a mistake. The initial vision behind Chronicles was that it would be a "second core set", with a new iteration every other year rotating with the actual core set. Then it was printed into the ground so hard that you can still find a sealed pack for $4-5 two decades later. Secondary market tanked.

WoTC knows this was the case, and you didn't see a reprint set again for nineteen years until Modern Masters. After ending new additions to the RL in 1999 with Mercadian Masques, Wizards had a decade and a half of data relating to high-value cards on the secondary market that could be reprinted, and a non-rotating format that utilized them (Extended, which did rotate, and eventually Modern). After two iterations of Modern Masters, in which Wizards successfully created a reprint set of high value cards without tanking prices, in addition to plenty of supplementary products after those went from 0 to 60 circa 1999, we have Eternal Masters.

The way that Modern Masters and Eternal Masters is being handled is nothing like Chronicles. The Reserved List is doing absolutely nothing for Tarmogoyf, which is worth more than most Reserved List cards were when it was first implemented in 1996.

Yes, it was a promise regarding the secondary market value of certain cards. However, over the course of two decades Wizards has shown that it can, and will, take a different strategy, as evidenced with cards not beholden to the Reserved List. You cite Scalding Tarn and JTMS as examples, and neither of those cards is on the RL. Why the assumption that this same strategy wouldn't apply to a card like Mox Diamond, or especially a dual land?