As to the -1 TN, while I think it is possible to make too little of it, it's also possible to make too much of it.
A superheavy was never going to generate super high TNs anyway. Since you're covered in guns and want to lower your own TNs, you'll tend to stay at a walk or stay still so you're never getting a TMM, after all, and since these will tend to be deployed to hot spots they'll tend to be pitted against veteran and elite mechwarriors (though one can still imagine senerios where a Level II with an Omega as an anchor has to hold against a green company that thought it was on a milk run) so again low TNs. I suppose the key down side is that such mechs can't dictate range so they'll tend to fight at long range.
But, a 3 gunner in a normal mech who walks and takes a shot at that Omega at long range is looking at a 7 TN, vs an 8 to hit an Annihlator (and perhaps a 9 against a Banshee or Zeus that can put up a +1 more readily). It's a lot, sure (I no longer have all the percentages memorized, but I want to say 15-16%?) but not enough to make up for the fact that such a mech has perportionaly that much more armor anyway.
Which brings up the point implied above, that a superheavy with massive armor might make an intresting mech to just soak up fire. A 200 tonner could mount 100 tons of hardened armor and still a decent selection of weapons. Or, perhaps more reasonably 50 tons of FL armor, and not be reduced in speed and weapons too much (would hardened armor make a 2/3 mech a 2/2? how would that even work?).
Such a mech would make that TN choice a lot more intresting. Will I take a shot at an Omega over some 4/6 heavy or assualt at a -2 relitive TN? Probably, because I want thouse three GRs off the field. Would I shoot some sort of Ultra Great Turtle, even if it had the weapons load of a normal heavy or assualt mech, or that normal heavy or assualt mech even at a relitive +2 TN?
As to things to mitigate that, looking at the two mechs here (and thinking ahead a bit) I see a few SRM launchers, so smoke rounds come to mind. Beyond that, one only need find a good firing spot once, I suppose, and in a defensive psudo-turret setting you can have a few prepaired positions for your monster that can help negate that penalty (though one could still argue that a conventional assualt mech could be put in those positions just as easily and to more effect).
