Manticore at some point made a change to improve the performance on dict=keyword queries, when very large expansion. (ie when there are lots of full keywords matching the wildcard)
That fix, enabled me to switch to dict=keywords on most indexes. (although some of the bigger indexes still use dict=crc)
In short dict=keywords IS better in manticore, but still not that it completely obsolates dict=crc.
(althoguh I think Manticore v4, has a slightly newer index format. havnt well tested that, still using manticore 3.x)