The only problem I have with this is - aren't you more or less taking another Markakis gamble with a deal like that?
The offense finished 4th in the NL in wOBA this season, and you'd expect that number to rise with an extra month worth of ABs from Camargo and a Markakis upgrade. I don't have a problem with bringing Zook back IF the $$$ for Grandal goes where some think it might or the asking price for Realmuto remains ridiculously exorbitant, but a 3 year deal for Donaldson just screams that he's going to be "in the way" at some point - and maybe soon. I understand slow-playing Riley, but once he gets here Donaldson becomes an expensively redundant piece who you can't DH. Even if he's "worth" his contract, he could easily become another Julio - someone everyone else is only interested in if you give him away for chump change.
I get that some folks aren't fans of spending much on the pen, but I'd probably rather splurge on a surer thing at the back-end than commit 3 years to Donaldson at this point. If he's willing to take a one-year "prove it deal", I'd be much more interested - just don't like the idea of being stuck with him and not being able to get pretty good value for him.
I realize I've been higher on Riley than most around here for a good while, but I think the organization feels the same way - they certainly haven't done anything to signal something differently thus far.