Surely glueing it without also screwing it would be inherently unstable as there's no tenon & far less contact area than even a short tenon Gibson joint?
not so sure
The fender pocket has a wide base and 2 sides - the end doesnt count as end grain glue joins are very weak. anyway. Its relatively easy to get these 3 gluing faces to fit together really well and it provides more than enough surface area for a good join. it works on PRS and les pauls juniors (the lip on LPJ on the treble side doesnt add much stability over a similar join without lip). it actually ends up very similar to the surface area on a doublecut PRS - they have it extending into the neck pickup cavity, but they also have more of the neck free of the body.
With gibsons traditional tenon you have 5 seperate gluing surfaces that all need to be carefully fitted. together those gluing surface amoung to a similar area as the fender pocket - but they have the problem that its much harder to get them all fitting perfectly - and we have pics proving gibson dont always get that right. a full with tenon is much easier to fit accurately
having said all that, there are issues with gluing a fender neck in.
1. Finish - any finish or sealer on body or neck will hamper attempts to glue them together.
2. Manufacturing - often they have a little wiggle room - fine for bolt on necks but not for gluing in, you need a nice tight join - preferably one where you could dry fit the body and neck and pick it up without the body falling off.
3. heel shape - it aint pretty as it is
a lot of these problems can be overcome if making from scratch.
