Is there any difference between "comme toujours" and "comme depuis toujours"?
I see that on the Google Ngram Viewer that "comme depuis toujours" is much less used. Is that even a valid expression?
I'd say that:
Comme depuis toujours means as usual, and refers to past behavior: the current behavior resembles the typical past behavior.
Comme toujours means as always, and - at least in principle - applies to both past and future behavior. In other words, not only has this been the case in the past, but it is expected to remain the case in the future.
And no, I'm not sure that comme depuis toujours is "legitimate" frog-speak. ;-) But I've certainly heard it.