Both my certs have 3 CRs and plenty of epoxy. Neither was a minimalist build.
The amount of epoxy on the fin to mmt joint, the internal fillets to both the MMT and BT, and the external fillets should very solidly be able to handle the thrust of 29mm motors. Heck, on my 3"darkstar you're talking over 150 grams of epoxy covering about 33 inches of fins. Add in the fact the fin butt up into the fin slots, that's structurally sound by itself. (To be clear, I've got 4 CR's in there, and a tailcone that acts as a thrust plate)
I put them in all my builds, but I don't dump a ton of glue on them most of the time. Do they add to a rock solid motor mount? Absolutely. Do I think a lack of them creates a "no-fly" situation? Not if the MMT is properly centered and attached, and the thrust ring of the motor is positioned so it's right into the fin tabs, not just the motor mount. Obviously this isn't an ideal situation for a high stress flight. Heck, I've never even done it. But it's certainly possible and safe to do on say, a G76.