With errors in who Mary is, you’ll often find errors in who Christ is. The two tend to go together - which is why the Council that decreed Mary as Theotokos was all about Christology. Recall that, even using the same scripture, the Trinity was argued for centuries.
It continues today. Those who have a problem with Mary often exhibit heresy in their view of the Trinity: Nestorianism, etc.
If you don’t understand Mary, you don’t understand the Incarnation, and without that theology concerning Christ and the Holy Trinity is very often flawed.
D-fendr wrote:
“With errors in who Mary is, you’ll often find errors in who Christ is. The two tend to go together - which is why the Council that decreed Mary as Theotokos was all about Christology. Recall that, even using the same scripture, the Trinity was argued for centuries.”
I certainly agree with your statement. But error cuts both ways here. And if any individual doesn’t think so, then he/she is very likely in error that other way. There is no locus (doctrine) of theology of which this is not true.