Here is my suggested changes:
- NARC works through ECM while active.
- NARC on non-ECM equipped mechs not under an ECM bubble when the NARC hits:active 30 seconds
- NARC on non-ECM equipped mechs under an ECM bubble when the NARC hits: active 25 seconds
- NARC on ECM equipped mechs: active 20 seconds
- NARC Ammo bumped to 10 per ton. Maybe even 15.
With a 4 ton minimum weight for NARC (3 + 1 ammo), it should have a LOT of ammo. You should never need more than 2 tons of ammo per match.
This makes NARC useful, and at least partially keeps to canon (where ECM cancelled out NARC)