I use a sling with T, since he was little. Sometimes he would fall asleep in it, but usually I would know when he was getting tired, and we would go up to his room and do a slight wind down routine (he was already calm) and then he would go to sleep in his bassinet. Somedays we had a difficult day but that is normal with all babies. He loved to be held (and still loves his sling @ 17 months) and it was so much easier for me (and safer I felt in some ways)
I would say that so long as your LO is not sleeping in the sling all the time and it getting sleep time in the bassinet like you say, then it should be fine.
I plan on slinging the next one