OP is right, though I think I'd word the basic precept a little differently:
XL engines are a terrible choice if your 'mech is going to take damage.
Light and medium scout 'mechs can usually get away with it because their speed means they're actually not expecting to take damage. Long-range support 'mechs are generally trying not to be in the line of fire; they want to pew-pew without taking hits. Some flankers can get away with an XL engine because they're hoping not to be taking fire while dishing it out; they flank, someone else does the tanking.
Any fighting role not mentioned above is probably not suited to an XL engine. But people build their 'mechs to be the big hero, not to be the calm guy with a highly specialized but effective role. They build their 'mechs like they're going to be action-movie stars, not soldiers. But then again, the lore is full of 'mech pilots being drama queens anyway.