If a perpetual licence costs $250, then a perpetual licence should be granted, BY LAW, after 10 months of $25 Subscription.

I think it's a little more complicated than that.

For one thing, the "rental" cost is typically much cheaper than that. Photoshop used to cost $700 for a perpetual license. It's $9.99 a month now. You'd have to rent it for almost six years to pay the full price. (And there's ways to get it for even cheaper. Free months are often included with other items, and they sometimes have sales at Amazon, etc.)

Plus, you get a constantly updated version of Photoshop (if you want - you can use older versions instead if you prefer). And you can rent it only when you need it. (I don't do this with Photoshop, but I have done it with Premiere. Needed it for a project, rented it for a month, cancelled.)

I hated the idea of a subscription at first, but now that I've tried it, I love it. There is no way I would update Photoshop every year under the old system. Or even every six years.

I used to think I didn't need the latest and greatest version, but now that I have it, I'm using the new features. Like "content aware fill." That's not a super new feature, but the latest update really made it work a lot better. It's saving me a ton of time.

If they did want to make Photoshop or other continuously updated software "rent to own," I think people who want to buy out should pay a percentage, depending on how long they've rented, since they're getting the latest version, which they would not have if they bought a perpetual license six years ago. Or, they could not pay anything extra and get a license for an older version instead (assuming they've rented for at least six years).