Board Thread:Questions and Answers/@comment-39499199-20190517210308/@comment-33378883-20190523144054

If it had been the official ending, it would have been a serious contender for "worst finale ever". The TMNT fandom lucked out. Other fandoms have not been so lucky......

From Nickelodeon's standpoint, it's an AU (not that it logically fit into canon in the first place anyway). There's really no need to link it to the other stories. At one point, Nick even sent out a tweet that said "production order doesn't matter" with regard to the Tales season.

Technically, I would argue that the  main storyline ends with Owari (and the Kavaxas arc). It wraps up the whole Shredder vs the Hamato clan quite nicely. Season 5 was basically a bunch of "Tales"  that you could take or leave as you wish.