Ok, I'm awake now.
I was thinking of the Blue Jay-Firestreak, it weighed 300lbs, a sidewinder weighed 190lbs and an R530 420lbs.
Correct me if I'm wrong but as I understand it the FD proposals were not making the small FD2 into a combat aircraft but making a bigger aircraft more along the lines of the F106? The 103B had the same wing but a bigger fuselage and the 103C used this bigger fuselage with 50% bigger wings. Certainly the Gyron and RR 106 & 122 engines are in the class of the J75 of the F105/106. So they aren't going to be Mirage alternatives, just like the Lightning wasn't.
You are right. THAT inflation of engine and specifications and size is unwelcome because it drives the cost upward. Although the Phantom sold pretty well, the F-106 did not. Dassault and SAAB avoided that, quite simply: there was no big engine available, so the Mirage and Drakken stuck with their medium size and weight.
SNECMA worked on a "super Atar" with more thrust but it was canned by 1958. So no French F-106.
Dassault wanted a twin-jet, Rafale-sized Mirage, but the French government changed it into a bomber, the Mirage IV. So no French phantom.
ER-103 C/D is probably much less expensive than an Arrow. It all depends whether it is stuck in an interceptor role (IIIC) or if a strike variant is developped as soon as possible (IIIE, V)
Somebody must step at Fairey in 1955, and at gunpoint, tell them "stick with the Avon, proven and powerful engine"