When it comes to encounter deadliness, there is more to consider than just CR and XP numbers, at least to old school DMs who are accustomed to factors such as morale, and intelligence/organization.
On one hand, skeletons are relentless, and never break morale. They fight to the bitter end and are never intimidated. They cannot be parleyed with nor bribed. This makes them a bit more dangerous than an equal number of goblins of the same CR.
On the other hand, skeletons are dumb and fight without regard to self preservation. They will march straight into prepared traps and not flinch even as they watch fellow skeletons get ground into meal doing exactly what they are about to do. Skeletons will not run to raise the alarm or go get reinforcements. This makes them a bit easier to deal with than an equal number of goblins of the same CR.
Environment also matters. The world is not a featureless white room in which every encounter is a simple math vs math exchange. The world the combat is taking place in should matter and have an impact on how things play out. So you have discovered a resetting crushing trap in an old tomb? You could disable it, but you could also perhaps use it and lure those skeletons to come after you and watch as the trap does the work.
CR is a measure of deadliness vs character stats and abilities only. Player ability and cleverness can sometimes enable PCs to achieve victory against encounters that they should be defeated by strictly by the numbers.
