Teams are 100% entitled to rotate at any point of the season and it's just luck of the draw if you end up against a weakened team or not. Likewise the teams that are safe have earned the right to try to bring youngsters through, especially this season when there's been no reserve games etc.
It's unfortunate at best for the teams who are hoping results might go their way, but that's just the way it is. To be fair, we went to Dingwall with a bare bones squad and won 3-1, so our commitment can't be questioned.
Furthermore, a few teams picked up draws against us in Feb in games that might have gone differently had we not been completely shagged.
Finally, and this is the most important point, if it was actually imperative that all teams played against balanced squads/consistent team selections etc then the transfer window would never be allowed to overlap the start of the season.