The trade off in BT is that less range = more raw damage, in most cases.
AC/20, ML, and SRMs are all short range with either high damage or efficient in terms of damage per ton. Late game, that combo can 1 shot any mech on the table with a called CT shot, or at the least cripple any mech without calling the shot. Using terrain and positioning against the AI, it's pretty easy to get into the front without even being shot--or only hit with some LRM indirect fire splash.
AC/10, LL, and PPC are all medium ranged. LL is more efficient damage/ton, but without stability damage. PPC and AC/10 are comparable, but with +dam AC/10 being better at random headshot kills and PPC getting the stacking debuff. In truth, medium range feels like it's the longest most fights end up taking place at, without intentionally working for it.
At longer range, the AC/5 and AC/2 are okay, but you have to build your playstyle around range to get the most out of it. That means rangefinder++ and/or a scout mech with sensor lock. You end up playing to grinding people down from range rather than punching big holes each turn. Of course, at this point, LRMs seem far more useful, other than their damage spread.