Thunder:
This is mostly useful at lower levels. While I don't think it needed to be removed (and am confused) at why it was; it is not a huge loss. For SCH, you can easily replace the 2.5 sec 70 potency (30+40) with a 2.5 sec 80 Ruin. In particular if you are not worried about MP, you can Ruin II (instant) and go back to casting. As far as WHM goes, for the same casting time as that 70 potency, you can do an additional Stone II for 170 potency. Lastly, at 212 mp cost, it is also more expensive than the alternatives.
Additional Note: This would be far different if All DOTs were included in Fester or Bane, but they are not. That being said, I also think Miasma II should affect Fester.
Medica II:
On first glance, the issue seems to be that you basically get a 50% reduction in HP regen provided you constantly keep it up. However, Medica II is MP prohibitive, costing 665 MP every 15 seconds. I believe it was nerfed to help adjust the concept that you can have 2-3 healers Keep up Medica II and regen on a tank/party with Bard song and heal through just about any type of Rage AOE (such as T4 Dreadnaugh). In order to stop people from doing this, the action allowed them to fix this without reducing the total amount of HP healed by a single cast of the spell.
Cure II/III:
This change to Cure II/III is created to make us want to rely less on Cure II and more on Cure III. As it stands, most WHM spam Cure I using Cure II only when it's free (or if you need a big cure) and Cure III, pretty much never. I can see how they would want to adjust it, but I also don't think it accomplishes what they want. WHM will probably stick with Cure II and end up spending more MP. The truth is that even with the radius change, Cure III is just too MP prohibitive. In most situations that require high intensive AOE, the party tends to move around more than 10 yalms (eg: Titan, ADS, etc). The only current content I can see that being useful would be in Twintania where you need to cure though very intensive AOE where the party members are already purposefully clustered. Given how Succor works, I think this would be much more useful if the radius was put up to 20 (so you might use it on its own), and or the proc from Cure II also reduced the MP cost.
Holy:
They only reduced the total potency by 16.7% but not the effectiveness of the Stuns. In the end, most of the things we use this for will not change. My theory is this was done to compensate for the addition of Blizzard II. In most of the situations where you would use Holy, you wouldn't spam it without a few second break between casts because it is so expensive. However, now you can alternate Holy with Blizzard II which will actually add to the semi-stun lock state (eg: Stun 5 sec-> bind 8 sec-> stun 3 sec-> bind 4 sec-> Stun 1 sec-> Bind 2 sec). This is evidenced by the fact that the new addition of the Blizzard II spell's potency (after change) is almost the same as holy before the nerf (200+50 vs 240).
Additionally:
I would make the point that WHM DOES need adjustment. The truth is that WHM has issues with hate and MP. There are plenty of instances where SCH has a large advantage in both of these categories. This is highlighted (beyond the current issues) by my comments on Holy above. While a WHM can alternate Bliz and Holy now, it will again increase the MP usage. I would personally like to see something to help balance out the imbalances between this (Shroud of Saints vs Aetherflow) as well as lustrate vs benediction. I believe reducing cooldown for Shroud of Saints to 2 min or less would do wonders to alleviate this.
Thanks for reading!