The purpose of tacks has changed but it doesn't make them useless.
i16, -6 on block, +12 on hit, full combo on ch. forward range is better than it appears.
To me this shows that in a matchup where ws k gets punished hard such as Cervantes, ivy, natsu, anyone with fast ce , tacks are a better option. Sacrificing 2 frames of speed for safety and the same reward. -6 is small enough to run reverse mixups as well.
There is also the use of normal hit tacks against the wall or edge as a tech trap or block/whiff punish for the instant ring out.