Certainly can be one or both of those as well as RRR’s vacuum leak.
It can be difficult to get enough initial timing and then slow the curve down enough to not get it rattling on top in or killing power around peak torque.
You really need to be on a dyno where you can load the engine at different rpm and load to sort out what the timing curve should be.
I have spent several hours just getting the curve right on some of these distributors and so far, the most difficult distributor to get what I want is any with a GM advance mechanism.
That is my least favorite one to tune. Actually right now the Chrysler stuff is harder to do but when I make a fixture to hold the weights so I can modify them then it will be easier than the GM mechanism.