The 49ers are top heavy but that is how GM Lynch built them. Ironically that is how the early 2000 Bucs were as well as Steelers which is why the Bucs back then were called paper champions for a long time until they won the SB.
With that said GM Lynch has quietly been building the depth because the Achilles heel of the 49ers has been lack of depth for a while when trying to make playoff pushes. So the 49ers have been kicking rocks on a lot of reclamation projects and lower round drafted players to develop for depth.
For example the 49ers nabbing Ricky Pearsall is a sneaky good addition because they have Aiyuk, Deebo, and Jennings. Your 4th, and 5th target on offense has to provide an edge. The 49ers can do that even if MAC isn't on the the field. Or, with Kittle they can really spread teams out and it is hard to defend.