It wasn't a waste of time , I started watching AOT since 2013 too , and it was such an exciting and enjoyable moments . why would you deprive people of having it too , at least for the first 3 seasons . I personally didn't read the end yet and just watching the anime (I couldn't read your part of the ending as it might contains spoil) but even if the end is terrible as you say this is not a reason to make the whole work look bad
RE: Why shouldn't you watch Shingeki no Kyojin? — eng/esp