I can't disagree that pneumatics are (slightly) more complicated than band guns, but I also don't find them difficult to service. Most are built to the same design, if not actually in the same factory, from what I can tell. Once you've taken one apart, you can probably understand any other. In fact, I'd be surprised if a simple pneumatic has that many more parts than a band gun. It's about 95% about o-rings with pneumatic guns, occasionally a piston replacement (readily available online), though you can get scratches to the barrel surface (replacements are available for many, as well). Even at that, a slow leak requires repumping now and then, but doesn't always render the gun useless for the length of a dive. They come apart and go together pretty quickly. The few that I've had and used with any regularity haven't required service, or even pumping, over long periods.
I understand the theoretical concern about depth, but I have yet to notice a practical handicap, though I don't dive deep. Also, you can simply pump the gun to work best (up to the limit of your ability to load) at deeper depths, if that's what you need. I was surprised to learn that the working pressure of a pneumatic is 300psi or even greater. A change of 30 psi in external pressure doesn't seem a lot in that context, and I don't even know how that aspect of performance compares to the inertial resistance of accelerating the water and shaft out of the barrel, in the blink of an eye. It may be that 50 ft difference of depth is pretty minor in the overall physics calculation.
I find pneumatics of comparable length to have more power than band guns, when talking about shorter sizes, 18-27" barrels. It's also true you don't see many pneumatics longer than 100cm, and few even at that length. At some point, spanning the length of both gun and shaft to load becomes unworkable. I shoot mostly at short distances here, and often among and under rocks, where a long gun is unwieldy. I also find loading a pneumatic to be more controlled, and less painful. They are definitely faster to reload. Most pneumatics of any length have two power settings. With pneumatic shafts, there is some proprietary nature to the rear fitting that has to mate with the piston (and some overlap in fit among brands), and two main shaft diameters, but those rear fittings thread on, so the shafts themselves are pretty generic.
I've heard some say that pneumatics make more noise. Maybe that's true, but band guns are plenty noisy themselves. If you really need to reach out, though, I'd say a big band gun is the only choice.