To be honest I think maybe the disappointing experiences are more due to the instructors and a poor approach to the classes,. There are huge benefits any puppy gets out of going to a socialisation class. The point should never be to do obedience in class the whole time and expect puppy's attention!!!
It's the difference between, say, a children's art class and an adult art class. Noise, messiness, disorder and FUN is the whole point!
This is all VERY normal stuff and exactly WHY puppy socialisation is recommended!! It is GOOD for them to be a bit unruly, meet other puppies, be distracted and gradually learn to be less so.
If the instructor wasn't encouraging fun interactions, and instead focusing on puppies having to learn things in such a class -- well, that's just plain sad and stupid. Especially if the instructor in any way made people feel the issue was their puppy not being somehow up to the mark. :sl*p:
One major problem is that basically anyone, no matter what their level of experience, education in training, qualifications, or personal stupidity, can offer a dog training class. So most are mediocre, most are based on training theories developed from outdated, poor early research on wolves and dogs now accepted in the professional world as being WRONG but totally underlying most obedience (corrections/dominance theory) classes. Most are offered by people who haven't a real clue about dogs, canine learning, working with students or dogs correctly... the list is endless on the problems with dog training classes. Just because someone likes dogs doesn't make them a good trainer! But that is the general level of 'qualification' most have.
It's why I recommend people only do classes from CPDT or APDT certified instructors -- the former is the better qualification now in the US but either is good outside North America (based on how people are certified -- it's far more open now in the US and less of a quality mark).
If the instructor isn't that great, I'd focus on letting a puppy just experience the class as the meeting other dogs./humans part, and doing some early fun obedience with a room of distractions, is all good. Socialising like this is what GOOD instructors consider one of the single most important things owners can do with a young puppy, so it is well worth doing a class (I'd consider it essential!).