First off just let me say that I dont fight MT but I train some MT because I fight MMA so I will give you the run down (in my oppinion) of your question from an MMA fighters perspective. Thats all the advice I can give you.
It depends. Guys also dominate by being more compact and powerful. MMA is awesome in that you get to create and taylor your own game in regards to your weight class, height, skill set, limitations, and strengths.
What would be better for you? To be shorter, more compact than everyone? or taller, longer, and have reach on your opponents?
Its about your game. In the end its all about your style and where you fit into MMA.
I know if I was 5'8" i'de be trying to fight at 170lbs. Personally. So your actually right at the propper walking weight. You actually may want to try and strip your body of the extra fat you might be holding onto (if any) so that you'll come into your fight at a solid 170lbs of muscle. I cant see how being made of almost pure muscle when fight time rolls around could be detrimental to your game plan in either event.
"Aure' ye' avin' a giggle at meh'? ... Ull' bash ye' fuckin' ead' in mate. I swear on me mum." Gypsies talking shit. Better than any stand up ever created.