I think this is a perfect example that newly certified divers have no real idea what to expect from the dive community, but have some preconceptions. You learned some important lessons, take them to heart, as it is your life, as well as your good time on the line.
First, nobody on the boat is going to volunteer much, especially newer divers. You want to step up and ask people to buddy up, and let them know exactly how new you are.
DM's unless secured ahead of time are looking out for the whole group, and leading the dive. That you had 2 on a small boat leads me to beleive the whole group was new, maybe they all took the class together and you got the last spot. You pretty much had you own DM, but do not expect that with out paying for it next time.
You should have done backrolls in class? Simulated at least? Some classes let on that we are one big happy family that reads minds, but that isn't the case. When the briefing touches on something you are unfamiliar with, or concerned with, speak up. Somebody WILL help you, but you have to ask first.
Alot of ops in developing countries will not bother much with certifications. In fact you could easily find a dive op to take you on dives to 150 feet on a single 80 straight out of OW class. You MUST know your limits and discuss things with the op before signing up, or you may find yourself on a "trust me" dive, and "trust me", you don't want that.
Unfortunatley the learing curve is steep. Most OW classes do not much more than introduce you to the gear and techniques, the rest is up to you to really learn. In the meantime the dive community is an eccentric, some of us are easy to get to know and very helpful, and some are downright nasty and will flat out complain and refuse to dive with you because you are new.
If you can hook up with some of the good ones who can show you the ropes, get you some experience, and have a good time with. If you can't find a club where you live, maybe you can hook up with a couple of people from here.
Getting back to your original questions, are group dives common? Yes. Are they safe? Yeah, no more or less than any other diving, just make sure you are within you limits and comfort. Was your dive op less than should be expected? hard to say. They should ask for a c card, but there is no law that states this, and so they do not have to. Most do though. That no DM helped on entry, well you should have been prepared for that in class. That a DM was right there with you was the right thing to do. I would say they are not a bad op.
Good luck...