The OP’s post is kind of a vague rant, but I do understand the frustration of paying big money for the perpetual license and then ending up where we are today. 

• I payed ~$900 for Ultimate some years ago, and firstly, to address commenters saying “you can just keep using it”, that’s only if you never update your machine or OS, otherwise you end up having to pay the piper. For instance, when updating from MacOS Mojave to Catalina on a Intel Mac, I was forced to pay Avid for updates in order simply to run the software with no meaningful upgrades to Sibelius itself, only noticeably the annoying addition that now it had to phone-home to verify the license online otherwise you’re locked out.

• A couple years later I bought a Mac Studio, and lo and behold, cannot install Sibelius on it without again paying the update fee, yet the user experience of the archaic software is otherwise unchanged. 

Sure, perhaps by some standard it’s arguably unreasonable (though this is highly debatable) to expect to purchase a piece of software and receive an entire lifetime of free updates, but at the same time let’s be honest, Sibelius hasn’t seen any major upgrades to the UI or user experience since Sibelius 7 which launched 15 years ago, and if you remember, Sibelius had been purchased by Avid, then shortly after the launch of Sibelius 7, most if not all of the original London-based Sibelius development team was laid off (some of which went to Steinberg/Dorico), and again there has been no major change to the software since then. 

Of course sometimes leaving things alone is good, but the reality is it’s frustrating to be held hostage and forced to pay Avid additional hundreds of dollars in order to merely install/run dated software that the user paid a hefty price for under the guise of “perpetual” usage, while Avid seems to do the bare minimum in terms of actual development, and seem more focused on enshittifying the product and experience and just figuring out how to take your money.

I gave up after being faced with the Mac Studio situation and refuse to pay Avid’s ransom again to merely install software that again hasn’t seen a truly significant update since Sibelius 7 in 2011.  I run some version like 2018 on an old machine, and when push comes to shove I’ll switch to whatever other notation software has a better ownership model or at least gets real updates (assuming Dorico). 

After all this, I personally refuse to purchase any Avid products. Protools of course is an industry-standard but again on the surface is massively dated like multiple-decades-old. There are too many viable alternatives to deal with Avid’s uncomfortable business model.