Sorry to hear this has been an issue for you. The reason this happens is because the files are already present at that point, as its those new files that its checking against. We do show in the release notes that the minimum PHP version has changed, and this is something you should always check before a major upgrade generally. What the requirement checker there is for is to tell you what you need to fix in order to move the upgrader forward, however it is very much in the upgrade process. The only way back at that point is to revert to backup, or fix the issue in question.
This is not the case. Im not sure where you got the impression you are not being supported there. The answer to your question would be to update your requirements or revert to the backup taken before you started the upgrade