Yep. Even without any injuries it's problematic.
If someone doesn't turn into a good backup for Garrison, that probably means Leaky has to slide to the 4. So then we need more backup at SF. BRob is the obvious choice and gives him more minutes (assuming Keeling starts at SG and BRob is his backup) but it's still going pretty small (Garrison will be on the bench, Leaky at PF and BRob at SF).
Do the math. If we're thinking Leaky will play 25-30 mpg and he has to play 10-15 at PF, that could mean BRob has to play starter minutes at SF. That could be nice for Andrew, since he'll get more PT at SG but, again, we're going deeper into the bench and getting smaller.
Similarly, if Sterling or Huff don't step up - and especially if Armando can't play long minutes - that means Garrison has to back up in the post. Meaning even more minutes for Leaky at PF and rippling on down the lineup.
Of course we could get Lucky. Sterling or Huff could make big strides over the summer and become solid post players. Meaning Garrison doesn't need to play center. Meaning Leaky plays less at PF, and so on.
But even if Sterling/Huff get enough better, we're still slim at SF. And, as you point out, that assumes no injuries. And some games we'll have foul trouble, or someone has the flu, or someone just has a bad game. And then being thin in the SF and PF positions could really hurt.