I have mixed feelings on this.

I feel that it makes sense and is ok to have Savage-specific phases for bosses. A8S is a great example, very well designed fight, and you get a brand new form at the end, yet the normal encounter still feels very complete and satisfying.

For the SB raids though, it is quite cheap for them to play on the nostalgy cord. They're taking final bosses that people already know, yet holding a majority of the players to see their final form that anyone who has played those games was expecting to see. It is in some way ok for O4S as the normal encounter still feels rather complete. But O8S just ends so abruptly and feels incomplete.

It will probably be OK in O12S (assuming Omega is the final baddie) because although Omega is known in the series, it does not have an iconic form that people are expecting to see.

In short, I think it's good for them to have Savage-specific forms when content is FFXIV-specific, but NOT when it's throwbacks to old FF games with well-known bosses.