fights will go to the ground sometimes, yes. but in the streets the last thing u want to do is stay on the ground and wrestle with the guy. if somebody took me to the ground, i have basic BJJ skills so i'm not completely lost. but i won't want to stay on the ground and wrestle with him. that's sport fighting shit like UFC or pride or something. i would just eagle claw his throat, hip bones, or ribs. if worst comes to worst, eye jabbing, going for the groin, or bite him. it's useless to roll around to try and mount and armbar or some shit like that. by that time anything could happen. his friends could come beat u over the back of the head with a baseball bat. he could've found a sharp object on the ground and jammed it into ur gut. or done any of the above i said i would do.
and it's true. u can't just use dirty tactics u gotta have the basics down to save ur ass too. but from the sounds of it, this place u describe is like an mma gym. and if it is, u won't learn shit there. find a specialized place that only focuses on one or two arts and take it from there. u will learn a lot more and be a much better martial artist that way.
MT and BJJ are good styles. they will teach u a lot. but don't expect to be the best fighter in the streets because of those things as those are very much sport martial arts for the ring. even tho, of course i wouldn't wanna fuck with a guy that's trained well in both, it only covers so much.
and don't think lawyers are dumbasses. ppl know things now. of course they'd know what an armbar is, and of course they'd know that u used an armbar if u broke the guy's arm with one. and plus, if ur trained to a high enough level in a certain fighting style, in certain areas, u'll be legally required to go on record so they can keep track of u. see if ur abusing ur training or if any shit happens with u, it'll be used against u.
but by all means, if u think MT and BJJ are the way to go, do it. MT is a great striking style and BJJ is a great grappling style. both require high levels of fitness and will get you in shape. but don't be restricted, and be open minded. even if u become a master in both, there is still so much more to learn. for example, u might throw a punch and a hapkido practitioner blocks, and grabs u in a wrist lock. and when ur on ur knees screaming in pain, because of a simple fuckin wrist lock, wut are u gunna do then? consider all possibilities.