Theologically, I like your description that it is a high plane. It is, but it's a plane one must get to if he or she wishes to continue theological discussion and debate on who Christ is. Exactly as you say:
Mariology cannot be understood apart from Christology.
So the reverse is also true. In my experience on these threads where ever we find a deficient Mariology we find a deficient Christology. Always. If you unravel their theology far enough, there it will be.
A wise Protestant would approach the topic as you did and recommend.
I approach Mariology the same way that the Council of Ephesus did. It defined Mary as Theotokos to defend against Nestorius’s effort to say that Christ’s humanity was not united with his divinity.