Whispering Giant, if you haven't heard - the runway is being rebuilt this year, with new safety areas etc. so no, you're wrong, it is not the States trying to protect Aurigny.
The only reason I could think of why Flybe may not wish to send a 175 to GCI first is because they announced it in the middle of the huge Aurigny/Blue Islands merger kafuffle, possibly to put a spanner in the works (purely speculation, but rather a coincidence).
Aurigny's LGW route is profitable as far as I know, and they have got more than 50% of the market share. I doubt they will be too worried about the jets being reintroduced on the route because many pax won't even know unless there is a substantial amount of press, which there probably won't be.
I just can't help but disagree with you therefore.