All styles have their own perks and drawbacks. It is up to the designer to balance the features in a way they think is optimal.
The advantages to the socket are connection strength and strength of the thread inserts. It is really nice not having to rely on bolts for your strength/stiffness; barrel nuts make construction and repair simple and reliable.
The ability to use m6 bolts reduces drag from the head of the bolts and allows rounder bottom of the fuselage.
Hiding the inserts inside the connection also allows for a thinner mast and lower drag blend to the fuselage.
The disadvantages of a socket start with the fuselage. Removing so much material weakens the fuselage, resulting in larger diameters especially when using carbon. The connection is only as strong as the wall holding it.
The second set of flaws has to do with wear, seating, and stiffness over time. The socket needs super tight tolerances not to wobble. Most versions use a taper to fix this which works in roll but the lack of contact on the bottom surface combined with low taper angles leads to the connection settling as you ride it, leading to inaccurate pitch angles between the mast and fuselage. Steeper taper improves this but also removes even more material fr the fuselage. If you have ever come in with a loose front bolt this is the connection settling.
From my experience axis actually has a pretty good implementation of a socket design. The straight walls mean no settling. They have the tolerances really tight. After a year or so of hard riding you can just re pot the connection with epoxy and it is better than new.
For race specific foils using metal fuselages, the foot may be the lowest drag as it minimizes seam area on the fuselage. You can go pretty small with the slot if accommodating to thicker masts or requiring extreme strength is out of the picture. Look at Levitaz R series for a great example of this.
Now on to the foot style:
Foot style connections sacrifice ease of manufacturing and ultimate strength for a fit that is more consistent, stiffer over time, and smaller possible fuselage diameter.
A foot style connection is easier to assemble and disassemble. Most slot connections only work when everything is extremely tight. In my experience, if you don’t need a mallet to put it together or take it apart a slot connection is not working optimally and will flex. In contrast, the foot is only as tight as the bolts and way simpler to use.
The problem with most foot connections on the market is they are just under engineered. Connections with a small width or using m6 like f-one, Ensis, or mikes lab will not stand the loads of modern large high aspect wings and large boards. Afs and especially duotone are much stronger. When looking for a foil using a foot style connection, I would set an absolute minimum width of 20mm and 2x m8 bolts. For anyone pushing hard, I would want closer to 30mm and at least 2 m8. I recommend using 316 stainless or better bolts.
A well designed foot connection will wear in. High spots will experience more pressure and wear down, spreading the wear to match the load. They can wear asymmetrically but this can also be fixed with a sanding block.
Foot style connections are easier to make with carbon. They have no thin walls, fewer sharp corners, and more robust cross sections.
I am also a fan of hybrid foot/slot connections like phantom uses. These still require strong bolts for stiffness but don’t rely on the bolts for maximum strength. Inserts can also be done with a barrel nut like the slot connection allowing a thin mast all the way to the fuselage.
The disadvantage of this design is it will need a larger fuselage compared to the foot only and it may be harder lay the fibers in the mold.
The last popular style is zero mast to fuse connection. Gofoil and Flite use this option. This can increase the size of the mast piece and make traveling difficult, or the designer can move the connections close to the mast, increasing the force on the connection. It also makes the mast more expensive and loses the option of a one-piece wing + fuselage and the ability to change fuselage diameter to suit foil purpose. I think there is potential for something cool with some more experimentation.
A few brands are more unique like Armstrong and gong but these would require their own individual breakdown.
In summary foils are a structural nightmare and we are not by any means close to a perfect system. Buy something strong or something with a great warrantee 