If you have a VSTi followed by heavy plug ins on a record enable track that is routed to busses with more plug ins that feed a master with half a dozen demanding mastering plug ins, then yes, 1 core will overload while others are not doing much.
Right now, that is the same in Logic Pro X and Cubase. And probably every other DAW. It’s very hard to load balance that sort of stuff.
My 5 GHz i9 9900k is very good at this(great single core performance) but I can still overload it fairly easily with my 6-8 favourite mastering plug ins.