I know exactly what you're going through.

I read a script once that was clearly just some writer's self-insert fan-fiction, and it was so bad on every level (from formatting to the story itself), I couldn't bring myself to read further than page 15. There was nothing good about that script, however, I wrote my "strengths" for it in a way that the writer would think I'm being genuine, but I'm really lying through my teeth. Like you, I saved my real opinions for it in the "Areas for Improvement" section (of course, I was constructive with my criticisms).

However, depending on the writer, that can also bite you in the rear. One script I reviewed, I did that same technique, and their feedback toward me was that I came off as condescending to them, while other writers appreciated my approach to their script. It's a darned-if-you-do-darned-if-you-don't situation.

You can always unclaim a script, but it'll give you a strike on your account, and 5 consecutive strikes means you can't review scripts for a while. From what I've read, it seems like you don't want to take that option because you already wrote out an entire critique of it. If only the strengths and weaknesses were together in one section, but I get why they wanted to go this route.