Arguments 1 and 2 boil down to the same problem: XL engine. The reduced survivability and increased cost of a heavy 'Mech with XL makes it unattractive in my eyes. In exchange for the staggering tripling or quadrupling of the total price tag, the speed and firepower increases which the lighter engine allows make the 'Mech about 1.5X as powerful. For the rare "Elite" pilot who can use that advantage to turn the tide of a larger battle, it may be worth it. For the "Regular" 'Mech jock, that's a monumental waste of funds.
I'll gladly take 3 non-XL heavies against it any day of the week, for a lot less money, and even give you a 1 step better Mechwarrior to pilot the thing. With three locations to take engine hits, expect a short fight.