An F/O with any more than 6 months seniority should EASILY be able to hold 14 days off. If he is holding less than that, it's his own choice (probably because of a difficult commute).
I detest MEM and dislike being there much at all, but I'm staying in that domicile because the trips are built commutable for the most part. I can hold an extra day or two off in DTW or even MSP but half the trips are uncommutable so I'm back down to 12, 11, or 10 days off... no thanks.
Additionally, as someone mentioned, more flying in DTW and MSP that needs covered so as a MEM pilot I can routinely trip improve into a DTW trip, thereby flying more hours over the same number of days and being in less of a "Greater Northern Mississippi Flying Club" mentality.
The Association (union) isn't fantastic, but there is a SLOW changing of the guard taking place to get rid of much of the "senior guy's mentality"... but as proven by recent LOA's, the progress is VERY slow.
Don't count on a lot of things they may tell you, such as:
1.) Quick contract resolution. Not bloody fu*king likely.
2.) More Aircraft. Again, not a likelihood when you do ANY research on the NWA family of regionals and the "whiplashing" that goes on every few years.
3.) New aircraft on a new certificate. Sure, it's possible, but we won't be flying them and will spend a year or more in grievance against it a' la' Mesa / Freedom - TSA / G0 Jets.
4.) 14-day off lineholder. You're coming in at the end of a LOT of growth, which means you could get stuck on reserve for a VERY long time in what is considered the WORST airline reserve system in the world.
Upsides: good crews, good coworkers, decent aircraft, good maintenance, and good pass / medical benefits (as compared to many other regionals or charter/corporate alternatives).
Good luck!