the problem with the balance is that substrate T2 cost less metal than phc. this air problem is just the tip of the iceberg, the devs are ignoring this completely. They make mauler cost 40 more metal and its problem solved. It;s not by far, substrate it's broken at the cost level.
Their economy its too strong and because of the metal issue they bring more workers to the table and kill you with superior economy:
Here is a link I hope Draginol takes a look at this:
edit: here is a link: https://goo.gl/s2ijgx
had to use a link shortener because the forum would auto correct the link to smiley faces!
Point is if you make substrate have versatility and allow them to produce air and cruiser from the same building than their units should drain at least as much metal as the phc. I real life versatility has a cost but in this game, devs have given substrate almost eveything, starting from less cost and going to better stats on substrate units allaround.
ps: das unding is really a cool guy for making this, I much appreciate his videos, he was the first to record the dominator / avatar problem.