Unfortunately, what you're going through is not unusual with Montblanc/Minerva service. Several members here have reported similarly long wait times, often exceeding a year, particularly for complex movements like the rattrapante.
A few key points based on past discussions:
Limited Watchmakers: Montblanc seems to have very few watchmakers dedicated solely to servicing Minerva pieces. That significantly slows down repair timelines.
Summer Closures: The Minerva facility usually closes for an extended summer break, which can stall ongoing work by months.
Quality Control Issues: There have been cases where watches returned after service still had functional problems, particularly with the chronograph reset function (as reported by @penfriend regarding the 13.21 caliber). So a thorough check once it’s back is highly recommended.
Your frustration is entirely justified. You’re not overreacting—this level of delay, especially without proactive updates.
Montblanc: It Is Disappointing And I Can Relate