I think the issue is, that once you get down to two fit front rows (of any position), or 3 second rows, etc, then as the injured one gets fit, another gets injured, leaving you always playing catchup.
Our problem is that we started the year (as we often seem to) with a few players who were possibly going to have to or want to retire or move whilst still in contract.
That has left us weak in the front row, back row, centre and wing. Any injury in those positions and we are struggling. We did have a bigger squad this year (was it 47 or 48?) but there wasn't as much quality in that and certainly not the quality in depth that was needed. Multiple injuries at scrum half have caused us a lot of problems.