Still, this plan is completely insane
By reasonable standards, yes.
However, if states representing only 7.8% of the population (actually less) can block any constitutional amendment and are incentivized to do so, what exactly is a reasonable standard?
What exactly is the alternative plan for reform?
The only alternative plan I have heard is no plan (simply to not have reform).
If in another 100 years the population of California has reached 200 times that of Wyoming, will that not be a problem? If so, what should be done about it?
If not, then you don't want reform. But in that case, the reason why you don't want reform is simply that you don't want it on the merits, not that you don't like the particular procedural plan to achieve reform.
Start by admitting each of the overseas territories and (the populated parts of) DC as states. Then reevaluate after a decade or so.