Well my problem is both toss and zerg can "macro it up" faster unless you risk an extremely vunerable fast expand and you cannot mech when behind economically. That and the potential of mech at higher ranks seems limited because their mobility is the most limited and lacking huge AoE damage.
Now the number one response to that is "OMG TANKS!" but I'm not seeing it anymore given their damage. It takes a huge amount of mech to hold a line and given general mobility in the game, you can usually force the terran to stay home to stop the "tank push". Thrors really have crappy AoE ability given the magic box trick used by any self-respecting zerg, helions are still great but only in certain situations given the famous helion drop got pretty nerfed given medivac speeds.....
Fungal growth, storm, banelings, colossus.....tanks just seem *eh*
In the end, I always think "man if I had bio, I probably would have won that" - marauders are a bit easy to use and extremely deadly. Having reached 1900ish diamond and heading down with mech to 1700s, and back up with bio.....I should really stop using mech but I just love it...and hate it Thoughts?