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jlmcmillan1978 just put racing brakes on, then you have to run low bias / power settings, and it's just about as sensitive to locking overall as it was in GT5 - only much more "grabby", which you would expect from larger rotors, for example - might be placebo, much as the slight reduction in grab at speed (due to increased rotary momentum and rolling resistance) could be, as far as the feedback from the game is concerned (you can't feel the deceleration, or the way it "builds").
The other alternative is just to turn the "bias" up to 10/10 with stock brakes. If you want the ridiculously unstable, dynamically (weight transfer) rear-biased brakes found on many cars in GT5, try something like 5/10. Also be sure to try these things in an environment where brake bias adjustments are actually honoured by the game: I use time trial in arcade mode, personally.
You're complaining about a wholesale sweep change in braking behaviour, when in reality it's a small tweak to the range of braking forces, such that cars now have sensible bias settings, if not overall power. The sensible bias is great if you've got the pedal range for the low power (it's a pain with my load cell, yet I can still lock up during trail braking), but the reduced power is clearly designed to make it easier for DS3 users to get into the joy of ABS 0 driving.
The underlying behaviour you're describing is still there if you look for it, it just interacts with the other physics changes in GT6 over GT5 in wholly pleasing ways now.
EDIT: tyre choice is massively important here. I use comfort softs usually. Anything above that and the default braking power is not going to be sufficient, except in trail braking. If you're using sports medium and above, try the racing brakes, or just increase the overall braking power in the "bias" option. Honestly, that should have been your first port of call.