If it were me, I would sacrifice Mid-Length gas system in favor of good quality 1-7 barrel and other milspec components.
The mid length gas system has some theoretical advantages, but there is no "spec" for it. Everyone does it differently.
Interestingly the Mid-Length gas system was invented quite a few years ago by Armalite based on work done at Crane by the new owner Mark Westrom.
It wasn't even on the radar until BCM started making them and getting them "pimped" by several famous trainers and then getting word of mouth marketing on internet forums.
Having a barrel that will shoot any weight or gas pressure round out there is more important to me than having a gas system that might get me 18,000 instead of 15,000 rounds before I break something in the upper. (Some midlength gas systems don't shoot low pressure .223 rounds well) By the time I shoot that many rounds out of it, I can afford to buy a whole new upper.
15,000 rounds at $.30 a round is $4,500 in ammo....