Correct that the output section is push pull, the difference between the inner and outer pairs in simul amps is that the inner pair is setup for pentode Class AB, and the outer is setup for triode Class A. In a push-pull Class A output section, tubes are biased at max plate dissipation at idle and the bias is half way between cutoff and saturation. In a push-pull Class AB output section, tubes are typically biased around 60-70% of max plate dissipation at idle with the bias closer to cutoff.
Part of the challenge with non-adjustable fixed bias is that the designer has to settle on circuit values that would ideally work with a wide range of tubes. There is an inherent tradeoff here, where you may decide to optimize for a particular tube type. Back in the Mark II days, the values were such that the amp would work with four 6L6s, or 6L6s for the inner pair and either EL34 or 6CA7 in the outer. So that's three tube types in the outer position Mesa accounted for, and there are performance ranges for each of these tube types.
By the Mark III, Boogie seemed to have recommended that EL34s should be used in the outer. This is likely because they decided to optimize the circuit to support the tubes they were using at the time. 6L6s will run too hot in a circuit optimized for EL34s, which is especially a problem in the Class A sockets because you're already at max plate dissipation. So I would agree that if you want to use 6L6s in the outer, you will want ones that are lower bias current as you mentioned, but in general you will want tubes that won't be much beyond 100% dissipation at idle and ideally are biased half way between cutoff and saturation.
It sounds like you changed the bias to protect your tubes because you had longevity concerns with the high idle dissipation. The tradeoff here is that you may end up in Class AB territory, so instead of having a simul class (simultaneously running Class A and Class AB) you will just have a Class AB amp where the inner pair are likely to be running differently than the outer.
At the end of the day, if it sounds good, and you're not blowing up tubes, and you don't fry your output transformer, then all is well.
