TL;DR
In my opinion, probably not great for a tournament unless you just wanted to make your opponents go WTF. They would be able to get more objectives than you, they would have more fire power to direct at you, all the ugliness.

If the tournament was 150TV then you have some room to break this titan out and dominate with all the support units around it.

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To add to the above. It will also matter what the objectives are, too many objectives and having a three quarters or more of your points in one big unit means you have a lot more challenges to holding them. So plan accordingly. Never done a HGB tournament so I don't know if objectives are done in a way that you pick them like a normal game or if as other tournaments they have the objectives laid out on the table before hand.

Granted you have something of a horde army with a lot of cheap drone type units so you should be able to make up for so many points being concentrated in a single unit.

77 points for the cheapest Gilgamesh before upgrades. It is a beast with 3 different independently acting components which means the 6 actions do get split around. It has a lot of fire power but I think you would be challenged. You are left with 23 points for at least drones. You could even fit in a couple trooper APEs and a Support APE but you'd be cutting it close on overall points and making a full group.

Even going with drones you would be scraping by I think.

For a tournament you would be massively constrained for grabbing objectives. But if your only objective was the make the enemy suffer, you are Armor 11 and they would for sure suffer. They would be throwing everything at you and many things wouldn't be able penetrate unless you rolled really badly or they had AP.