i believe that a big roster would lose more in a situation like that because the players have more specific roles.
in a smaller roster your starters are the most important by far.
i think the second part of your argument is more important, normally my big roster can catch up injurys more easily since i have backup of nearly the same quality. In three of my last four games i lost a starting guard in the first quarter, i still won two games even when they was very close.
But with the outside offense my priority on the SF spot switched and normally i would have played at least 20 minutes with Nishnidatse - Nuno - Mabaquiao and wouldn't use my big so often on SF. This switch of the position makes my lineup at the guard/wing spot rather small. Also it changed my defensiv assigment, since i could have played 2-3 with the big rotating more often on SF.
the roles of my 3 guards ain't that different, they are all comboguards since i rate passing pretty high also so my guards usually can shot a bit and pass quite good(Nuno passing as a SG is already weak for me)