At level 100 it takes 110 crit rating to get 1% crit. Meanwhile it takes only 66 multistrike rating to get 1% multistrike -- so since multistrike is 60% as effective (as you mention), the two are effectively even in rating conversion.
Note also that while multistrike doesn't grant us any secondary benefit, in terms of ability damage it's about 17% stronger than crit just because we have 0 base multistrike and 17% base crit (assuming crit suppression is still in; otherwise 20%).
If multistrike rating were added now (on live), it would be worth taking (assuming other stats remained fixed) up to about 32% multistrike (11k rating pre-squish, or 7k beyond what Haromm's Talisman would provide) -- and that's with re-origination not working off multistrike rating. With a different trinket it would be even better (relative to other stats).