I am kind of in awe of the Ordinatus. They are some of the few Epic models I haven’t collected yet, but the whole army looks about as sturdy as wet tissue in the field with all your heavies having no void shields. How did it do?
Your right, the Adeptus Mechanicus are not the hardest hitting force out there and on top of that most of my forces are designed and built around the universe fluff rather than for tournament play. Though I do have a few IG lists just in case someone needs a stomping. :)
The game I played in at MillenniumCon was a 3 on 3 game so the AdMech acted in a support role (just like in 40k fluff) and they did very well. I run 7 Ordinatus total - 1 Majoris with a nova cannon and 6 Minoris (usually a tank fighting unit and an infantry fighting unit.) They are not the best bang for the buck but they are deceptive on the table - opponents see a handful crazy looking tanks with light armor but when they fire it’s like being shot at by a whole company of tanks.
As an example: the anti-infantry Ordinatus unit pumps out 12x AP4+/AT4+ and my anti tank can pump out 12x AP5+/AT3+ and 4x MW2+ so they can be fearsome if you get too close.
All in all they are good fun.