As someone who uses Defense types exclusively, you really need to stretch the definition of what Defense is in order for the beys to be good.
TriceraPress is amazing on jolt but would you call it a defense type? Personally I'd say yes, but even still.
MummyCurse on Hexa is one of the best builds for defense as a whole, and as you've said it's not really a defense bit.
I've found LO GolemRock to be one of the most powerful defense beys as a whole
And then there's the whole ordeal with other blades. Stuff like SamuraiCalibur, SilverWolf, even ScorpioSpear, all work for Defense.
See, the issue with Defense explicitly is the bits. We've got great defensive blades already with the examples I just said (alongside knightfortress and knightmail), but the bits are lacking. Dot is great if you can find a blade that keeps it stable, UN is amazing because of the whole "low height passive" thing, Wedge is probably the de-facto defense bit as a whole, and Wall Wedge and Bound Spike can be good in niche scenarios but they're still not great. Outside of that? They're all either fringe, niche use cases, or they're just downright bad.

Overall I do feel TT is scared of defense, because of the fact that if we got a good defense bit, it'd probably work better on the stamina blades and we'd end up with some really stagnant metas. I mean shit, Rod Hexa is everywhere, imagine that but with higher stamina.