Viper is much larger than Jeff.
Viper can load 4 AMRAAM at any A2G loadout(which Jeff will only left with 2*PL5 in most case), its 3/7 hardpoints already enough for many heavy wpns, its internal fuel can sustain quite a long time, its TGP/HTS does not need additional hardpoints.
But again, Jeff can do its own job quite well, and have some nice handy wpn such like the BRM-1, LD10, etc. It's a very good light multi-role fighter.:smilewink: