I can understand why they have increased coring costs in general, but not why they have reduced so much the claim discount.
Yes “carpet-claiming” was probably an issue, but you now have a situation where it is very difficult to core same culture, same religion provinces, which seems ahistorical to me. A better solution, IMO, would have been to change the claim system so that you could only fabricate a claim where you had a realistic claim based on history/nationality.
Take Muscovy as an example (my favourite starting country). A realistic scenario would surely be to have easy cores on the Russian lands and far more difficult coring of Horde lands. This would then also surely produce a far more historically accurate game, while also stopping unfocused “blobbing”.