I completely disagree with you. HVAC is not that lucrative and entry level would be more like $15 an hour. If someone cuts it they could make the $28 you describe after maybe 5 years if they are good. If your not in a union you can’t be an apprentice. I don’t know about the sheet the metal workers union but that is irrelevant because they are sitting at home right now. I can speak for the pipe trades union. A second year apprentice makes 60% of journeyman scale which is $28 and change unless he can negotiate something above that. There are at least a 100 union guys in town making over $35 and up to a dozen over S40. Probably a similar number or more (to compensate for lack of benefits) working non-union. But the vast majority of the guys driving the hvac vans you see on our freeways are making less than the 28 you describe, have many more years experience than the 2 you describe, and sit at home when there is no work. While HVAC has done better than other building trades the past few years because it is has more service work than the other trades which are primarily construction, it is still in a bad place and not lucrative. Essentially the building trades in So Cal have been destroyed.
I also find it funny that anyone would think the labor unions would care at all about anything residential in San Diego as they do zero residential work here.