Fates Warning are by no way playing it safe. They are nothing near what they were in their prime sound-wise. You compare Perfect Symmetry to Darkness in a Different Light and it isn't even close! Matheos has been pushing boundries for 25 years.
You're trying to compare a 25 year gap as your basis for defining "safe", and that's not what I am talking about..... Album to album, they have not changed SIGNIFICANTLY since the Arch / Alder change, with "No Exit" serving as a mid-point. There has definitely been evolution over that time period, but it's been a gradual one.... Symmetry morphed to Parallels, Parallels and Inside Out were virtually the same album, APSOG was a bit of a departure into a darker sound, Disconnected took the APSOG theme and added a bit of OSI/modern element, whereas X brought them back a little more into the Parallels style, and Darkness merely carried on from there.
My point in saying they played it "safe" is that they didn't release an album that was a dramatic departure from what came before it, or from other material Matheos had been working through (OSI, Arch/Matheos etc). Sonically, they are all fairly tightly knit.
Absolutely they have changed over great periods of time, but each album segues into the next, and a fan of one is more than likely to enjoy the album before or after.
When I think of a band NOT playing it safe, I think of Opeth going into their modern phase, or Pain of Salvation doing whatever the hell they are doing now.... A band that turns their formula on the head, surprising and possibly alienating many of their fans in the process.
Fates writing has never been "safe" in the sense that it would capture mass mainstream interest, or not challenge the listener in some way. Music can be challenging and safe at the same time. I actually thought this last week when listening to the latest Leprous album. It's technically complex, it's unlike anybody else I hear, but the last couple albums have felt "safe" in the sense that I know where each song is going before it even gets there without having heard it. They have crafted a certain formula that they are "safely" following, whereas if you listen to "Bilateral" that album is all over the freakin' place.....
I find the other bands above to be the same "safe". They aren't reinventing their wheel, they are merely evolving gradually over time from one album to the next.
I LIKE "safe" in most cases.
As for Maiden, I can't comment yet on the new album, as I haven't heard a single note from it. In theory, I agree that (based on song length) this may NOT be the "safe" I am talking about at all. I HOPE it's not. If they simply take the same formula from "Final Frontier" and crank up the song lengths, this will be a snooze fest.