If it was me, from what I read here I'd skip the additional testing parts and go directly to the "move on" part. But I'm kind of judgmental that way when paying money to supposedly professional service providers.
From the original description, the service person is either patronizing or lacking competence (or both). If it's the former, further testing won't change much, if anything, because the real problem is attitude towards quality and customer service. If it's the latter, you're spending your personal time and money to educate somebody who already should be more competent than you at delivering quality results from his own shop.
The initial results of crushed blacks and magenta cast are results I see & hear about pretty commonly from "commercial" operations, and indicate to me the printing system just isn't dialed in. (Note that I include the operating person as part of the system.) On top of that, the reported statements from the "pro" about image density, a 9000-series printer being "more accurate" than a 2880, Epson printers having an sRGB colour space, etc. range from hogwash to avoidance of understanding the real issue.
Further engagement seems to me quite likely to be a waste of time. If you have other alternatives, why not just go with them? If there is a reason why you need to consider this printing service for your needs, then you may have to go through a pretty step-by-step workflow breakdown with the "pro" to determine where the issues are entering, and to convince him to pay attention to fixing them...