Now you’re just arguing that the supernatural aspects are what’s “too convenient”, etc. All of Key’s settings are supernatural. The only difference is that with stuff like CLANNAD and Little Busters!, you don’t realize until towards the end that the setting was supernatural the whole time. Which leads to two things:
1) Shock-value and tearjerk-iness can be increased majorly with the “holy shit all that was happening the whole time and I never knew damn those characters are strong, etc.” But 2) it requires you to use your suspension of disbelief at the end, in the heat of the moment, instead of at the beginning when the setting is being built. This makes it seem more like an out-of-the-blue, “what the hell” kind of moment instead of something thats been building up the whole time.
Both of these affect each person in varying degrees, which is why some people like it more than others, and some people are bothered by it more than others.
As a side note, Angel Beats! seems to have the opposite set up, with all the supernatural stuff in the beginning, and all the real stuff hitting hardest. (From what I gather, Rewrite might be similar. I don’t really know anything about it, and I don’t want to know so don’t tell me)