I started looking into this in response to the constant claims that Mario Götze's transfer was cynical: That it was intended to hurt Borussia Dortmund rather than help Bayern; that Götze isn't getting a chance to play at Bayern and is instead buried on the bench (or doesn't have Pep's trust or whatever); and that he should leave in order to get first-team minutes. In looking into Bayern's rotation over the past couple of seasons it also got me thinking about what that means for this season's depth and rotation, so some thoughts on that at the end.
On the first point, here are the facts. Götze appeared in 32 of 34 Bundesliga matches for Bayern last season, tied (with Manuel Neuer and Thomas Müller) for first in the squad. Twenty eight of those were starts, which puts him behind only Neuer (and tied with Müller, Robert Lewandowski, and Juan Bernat). He was fifth in the squad in total minutes played (behind Neuer, Müller, Lewandowski, and Bernat). By every measure he is definitely a core, first-choice player at Bayern.
But, does he get to play in "big games"? Götze appeared in 11 of 12 CL matches (behind only Neuer and Bernat, tied with Lewandowski, Boateng, and Rafinha), with 9 of those being starts. He was eighth in total minutes (behind the above plus Xabi Alonso and Müller). So, there's a little more rotation there, but he's still definitely first-choice.
What about the previous year? He appeared in 27 Bundesliga matches, good for tenth in the squad (which saw less rotation). Twenty of those appearances were starts (tied with Arjen Robben for eleventh). He was eleventh in minutes.
Again, I'd say that makes him a first-choice player, but it's somewhere on the borderline between "first-choice" and "rotation" player. He appeared in 11 of 12 CL matches (tied with Toni Kroos behind only Neuer, Alaba, Lahm, and Muller), but just 6 of those were starts and he was 13th on the squad in total minutes, so for that competition, he's probably best described as a "super-sub."
But still, as a 21-year old in his first season with the club, he was borderline first-choice for league play and super-sub for CL, then as a 22-year old he worked his way up to core first-choice in both. There's no evidence whatsoever that Mario was bought just to hurt a rival, rather than to be used fully in putting together Bayern's best possible team, and there's no evidence that he's buried here or needs to leave to get playing time.
As for the lessons about squad depth and rotation, Bayern played 14 guys at least 1000 minutes in last year's Bundesliga (what we might call the "core rotation") plus another 4 for 500-1000 (the "peripheral rotation" players). The year before it was 15 in the core rotation plus 4 peripheral. And the year before that (under Jupp), it was 15 core (pushing Robben up into this group even though he had 999 minutes) plus 5 peripheral.
So that seems pretty systematic that we need about 14-15 guys who will start frequently, be named in the squad whenever healthy, and regularly sub-in in matches that they didn't get the start. Plus, another 4-5 are necessary who might get a rare start if there are injuries, fill out the back end of the squad, and get rotated in when we want to rest core players for mid-week matches, etc.
So, taking currently healthy potential core guys this year, we have Neuer, Boateng, Benatia, Alaba, Bernat, Rafinha, Lahm, Alonso, Kimmich, Hojbjerg, Rode, Vidal, Thiago, Gotze, Costa, Robben, Muller, Lewandowski. That's eighteen (I'm going ahead and calling Dante peripheral but am staying agnostic as to which of the young midfielders break into the rotation). And, if any/all of Ribery, Martinez, and Badstuber make it back, we end with way too many core players.
Except of course that we don't know in advance which potential core guys will ultimately end up outside the rotation (for injury reasons or otherwise). Last season we expected Ribery, Badstuber, Shaqiri, Thiago, and Javi (and maybe Pizarro) to be in the core rotation; Ribery and Badstuber ended up in the peripheral rotation and the others fully outside it. The year before we were less snakebitten by injury, but the point is to be prepared in case it happens again. It looks like this year we can have a couple of those prospective core guys fall to the peripheral rotation due to form/fitness/consistency, plus lose a few altogether due to injury, and we'll be right around that magic number of 15 guys in the core rotation.