Any column held rigidly at two points and supported up high by stays, as a keel stepped mast is also held at the partners, is more able to stay in colum than one held rigidly at one point and then with stays. You can look in any good NA text to see the difference in scantlings for a deck stepped versus a keel stepped mast.
A tabernacle is just a pivot for raising and lowering the mast. It is not a structure that even approxomates the strength of a reinforced by the partners hole in the deck. A mast on a tabernacle should be of the same heft as any other deck stepped mast, as that's what it really is.
Especially in small boats and with the reality of standard extrusion sizes it's not unusual for the keel stepped mast you actually have to be a bit over-strength and perfectly workable if you cut off a few feet and deck step. That simply reflects what people build, not engineering possibility.
G'luck
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