Well, again. We are talking about CLASS with instructor OP chose and pays to teach. It's not just a dive with some buddy. If you don't trust your instructor - find another one, if you do - do as he says. It's that simple.
Now. Learning how to feel comfortable WITHOUT pony, monitoring air, being aware of other divers, surroundings is BEST with the instructor. It's a class. This is where you learn how to deal with things without pony. As I said before - after the class, pony or no pony - nobody cares. Sling 2 ponies if you want to, but in the class it's the best time to learn how to deal with situations without pony. Why? Because in real life situation you have chances (although slim) ending up at 130 feet alone without pony; and if you have never done it before you have a very high chance of panicking and eventually getting into an accident. That's why when you are with the instructor you chose and paid you practice the worst scenario.
Later, during the "regular" dives - yeah, do whatever you want, but class is not a "dive", class is where you practice all sorts of possible scenarios that may happen in real life.
And I agree with the insutructor taking the student to 130 feet with 5 mm wetsuit on 50 degrees. Why? Because it can happen in real life. A person may get separated, be swept away by the current, get entangled, hit thermocline, end up in depth that wasn't planned. And if that person never done that, then there is a high chance of person starting panicking. So.. the class with an instructor is the best place to practice these extreme scenarios.
My friend had a class like that. The instructor took him to about 40F deep dive, everybody got narked, it was dark, few folks started panicking, but they handled the situation. The instructor had 2 more assistant divers. Well.. months later my friend ended up saving a panicky girl on a deep dive. He said "after that crazy dive we did, getting a girl from a 90 feet was piece of cake". My friend had about 30 dives back then, she had about 100. Eventually he appreciated that deep dive, he always said "at least I know how it feels being narced in dark murky freezing water, now I know I can handle it".