i haven't gone through every list thoroughly but every unit that has this are size 5 or larger (almost the size of 'light' TAGs or massively larger than regular in the case of the Scorpion and Megladon) and their weapons are larger than infantry versions, should fatality 1 be included within the heavyweight rules in N4?
Can I instead suggest removing Heavyweight completely? Its only rule involves Gates, and I've never seen anyone play those as written outside the Armoury due to the exacting requirements needing to be built into the scenery.
How do you mean "[not] play those as written"? I get people to define doorways as Narrow Gates all the time, and Windows as well when they let me. Doorways being Narrow Gates allows you to put S3/4/5/6 troopers through them Prone. Windows being Narrow Gates but elevated above the ground allows you to put S1/2 troopers through them but only when Standing; being Prone you can't get in B2B with the gate to pass through it. Heavyweight actually makes a difference if you do this: it makes things like Taskmasters much more mobile than things like Blackjacks.