Plenty fair, in my opinion. Adobe needs the features of Win 10 to acheive what they want with their software, and so to get these benefit (BENEFITS) for users, Win 10 is required.
But as with any computer software, it is your CHOICE to keep an old operating system and run the risk of software not operating properly. Again, that's not unfair, you have a CHOICE, and you make it and then claim someone is being unfair ... you could make a different choice.
But people will always complain. If Adobe did not make this choice, and were unable to provide the desired features for their users because of limitations of the old operating system, people would also complain that they were no longer getting the benefits from the Adobe subscription, and that other software now had better features. So I am very glad that Adobe continues to provide us new features, and that they are staying ahead of (or competitive with) other software.