As an instructor, I really only dive with my students. While I am on a trip that I am leading through the shop, I do give gear setup briefings, but leave it up to the specific boats DM to do the dive briefing.
Often, you can "tell" who is an instructor/DM, etc, by the fact they're not throwing their weight around. If people ask me (on my personal trips), I might let on I am an instructor, and will offer - if asked - them some pointers.
As far as "checking your tank", this is very, very standard on most dive boats. The deck hands do a double-check to make sure you've opened your tank. I, for one, assemble my own gear, check my own gear, etc., before the dive, but will turn both my tank, and my buddies, completely off until we get to the dive site. One time, I had a dive buddy - who professed extensive knowledge - actually turn my air totally off, then 1/2 turn "on", before we splashed (on a trip I was leading in the Flower Gardens). As you know, your 1st stage will work fairly well with only 1/2 turn "on' - until you get farther down. At around 90 feet, my T2 was breathing kind of ragged. I kept motioning to my buddy to check my air valve, and she couldn't figure out what I was asking. I handed her my camera, took my BC off underwater (around 90 feet deep), and found my valve almost off. I solved the problem myself. THAT is why the DMs check pretty much everyone's air before splashing, because some people don't know open from closed on a valve.
But as far as the rest of the gear, I don't know why they would touch it, unless you looked rigged incorrectly. I've had students assure me they're properly geared, only to see BC inflator hoses not connected, regulators improperly installed (the best was someone had the regs on the left side, no inflator attached)(fortunately, this was still in their pool sessions).
You shouldn't be taking any of this personally (a DM touching your gear), as they want to collectively ensure the entire group is properly geared up, so as not to cause any problems during the dive, in which they would have to call the dive for everyone. I find it highly annoying when I am on a required guided dive (sanctuary areas) and someone hasn't a clue what they're doing. Years ago, I was in the Galapagos on a liveaboard, and there were some Russian divers that were awful (only a few in their group, the rest were awesome). Somehow, these people had given false dive resumes, saying they had extensive experience in high current, limited visibility, and deep diving (they didn't). After our first real dive with some of the folks, there was almost a mutiny on the boat, that got the captain involved. The "real" divers did not want to boat with the wannabes (many of whom had horrible buoyancy skills), and insisted we not be put in the same group. The captain agreed, and the experienced group dove together the entire time.
So....with all of that, ask yourself if you are part of the problem. I have never had pushy DMs, deckhands, etc. Every place I have been in the world, the people have been very helpful (after all, the DMs are working almost exclusively for tips). Only one bad experience in Cozumel (with CozumelsBestDive) did I think the people were idiots (pretty obvious the guy in the water on the private night dive was clueless - I had to show him where the reef was, after he insisted on swimming up-current for five minutes while he was obviously lost, with no compass). If you're getting continually "checked out" beyond the tank valve, then odds are you might be presenting yourself as something the DMs are picking up as somehow under-qualified (they have a "nose" for that). This isn't a "flame", just pointing out that if there is a trend in this, you need to ask yourself that question.
The DMs are there to make sure everyone has a good time and - more importantly - it's done safely. Each of you is supposed to be an autonomous diver. Sadly, I have been on boats with people that have been diving for a very long time, and they are some of the worst divers I have seen (e.g. slamming the bottom, dropping onto coral, touching things, kicking coral, etc.). Even as an Instructor, I am always looking to be a better diver...looking for that perfect Zen, where I am moving with the underwater world as part of it, not some invader that is there scaring the fish, or damaging the environment. Hopefully, everyone is looking for that, where their entries, exits, and visits are movement poetry undewater.