I think that you've never played Cassiopeia before, or against a good one, and that you didn't even try to think precisely about this mastery.
This mastery is basically the end of mana problems in early game for Cassio. You do not seem to realize that her E costs 40 mana lvl 2, which is 10% of her mana pool.
If you clear the first wave, you have one more minion to last hit before getting lvl 2. If your opponent doesn't respect you enough, you can kill him lvl 2 without spending any point of mana. You do realize that, in 5 seconds, she can Q + 3 E + Q + E you ? A Cassio can already get you out of lane lvl 2. The problem is, if she does that, she spends all her mana and cannot play the lane anymore herself.
An even funnier fact : you set all the minions to low life before your level up, and last hit with your E during the 5 sec with Presence of Mind activated :
-> You last hit, so the mana spent is restored, as it is how Twin Fangs works.
-> You have Presence of Mind on, so the mana is also restored.
Basically, you last hit with E and your mana is restored of the E's cost. Not only you do not lose mana. You regen mana. When last hitting.
Nah, this mastery is obviously incredibly strong for Cassiopeia.
For Ryze, it can be, as you can Q W Q E Q freely, but that would require to be in closer range than Cassio, and it wouldn't be as easy to force a trade, while Cassio can stand between you and your minions to deny you and kill you if you want to last hit ( as she already can, but no one does it except in some specific matchups because of the mana problem, which is now irrelevant ).
What you want to look for, anyways, are champions with very high mana costs and low CD that would like to trade you early on but cannot because of mana problems. Here are some :
Cassiopeia ( Q + E spam ), Taliyah (W E Q ), Viktor ( W E Q ), Lucian ( E 2AAQ 2AA W 2AA ), Kayle ( Q W E ), Azir ( W E Q W, you cannot lose trade actually ), Jayce ( Range forme E + Q W R W Q 3AA E )...
All of them could be played with the Precision Tree as a second rune tree, so it wouldn't even be a sacrifice compared to the Domination or Inspiration tree.