I believe user friendly is a personal matter. I carry my shield 45 with the extended mag and never notice the gap, nor have I noticed any user friendly negatives on using the +2 base plate of the g26's. Even if the gap was noticeable, I'd still not buy a sig out of exeter. Last two I bought had to go back, their QC isn't the reputation the company was built on today.I agree- as long as that extra 5-7 mm are a contiguous unbroken space (like the g17 vs g19), or with only a tiny gap. But in this comparison of the g43x to the p365, photos show the extra 6mm of the 43x aren't very user friendly with the flare and gap, and the longer grip of the 43x costs two rounds compared to the p365 above.
I think you'd make a better argument if you just concentrated on the added round capacity of the 365 than the gap or flare.