It's not really clear to me where the balance stands right now (not to hijack the best topic on this board). It feels as though the main reason there aren't more energy mechs is because they rely on 3 or 4 really strong items that are legendary/mythical-only, and are therefore really expensive to make. Meanwhile, making a really strong physical mech requires no such luck/really money.
But yeah, hard to say. It'll be interesting when a few balance changes are made and more people actually have access to the best items. Right now who wins and loses is about 80% items/fusion level, 10% turns/initial spacing and 10% tactical skill.
What I'm looking forward to is when the game becomes more of the latter too.