It's all about perceived value.
GM#1 - Yakupov has proven he can play in the NHL and will improve every year. Though MacKinnon is said to have a higher ceiling, he has never played a pro hockey game and may not have an impact this coming year, or at all.
GM#2 - Though Yakupov had an excellent rookie season, I think it would be best to stick with the 1st overall pick. While there's more risk, a top prospect like MacKinnon can potentially eclipse Yakupov's success. The risk is worth the potential reward.
Plus, a GM with a high pick will most likely play hardball since he can simply use the pick and probably end up with a great player if his potential trade partner doesn't meet his demands.
I do agree that Rielly straight up would be a tough sell. It would probably take more.