There has been a Subscription Model for years; it is called the "Plus." I pointed this out in the earlier topic you already have running:

https://proconnect.intuit.com/community/proseries-tax-discussions/discussion/qb2021-desktop-accounta...

There is no need to start again, here.

Yes, it always costs a bit more to own it outright.

"On multiple computers this could add up to the tens of thousands for this new subscription model over time."

Yes, Subscription Service is a money-maker, which is why Intuit pushes the QB Online tools, over Desktop.

"Am I correct or is there a better option?"

I buy it outright and keep it forever, as you stated you have been doing. Amortize your investment over all the years, to understand its worth to you.

And you should ask at the QB Community, or Intuit QB Sales, and not the tax preparer peer community, for issues related to buying and owning QB.

Your clients are going to have a few problems: Every Windows computer is now going to be W10, and the older programs will stop launching. Their data files are falling further and further behind as to internal format, since the programs are both updated and Replaced with the newer year; that's why you are supposed to update at least every 3 years. Worse, each year, the 3rd oldest program loses updates and support. Every May, compute "current year + 2." So, May 2021, Intuit will only support QB 2021, 2020 and 2019. QB 2018 will lose all external functions (payroll, online banking) and no longer get any updates. I just recently launched QB 2018 to Get Updates, since it had been a while for my system. If I needed to get the final patch update for QB 2017, that would be done manually, and at some point, the files are no longer available. I often stash a copy of the final patch update for that reason.