For now I stopped playing the game, but I made some tests regarding Restoration, and my previous calculation is incorrect. The healing is not increased by +840 as I thought. Here are some data from my character:
Max HP: 46035
HP Regen: 625
HP Regen w/ Restoration: 1465
Heal lvl 15 Tooltip: 5% of Max HP + 268~402 (no tooltip changes w/ Restoration)
Restoration lvl 14 Tooltip: +840 HP Regen
Heal received per tile: 4202~4386
Heal received per tile w/ Restoration: 4624~5056
Now, the things start to get weird when you make 46035 x 5% = 2301. Even if you add the additional healing from Heal + HP Regen, I have no idea how the tiles are healing me for at least 4202.
Also, with Restoration my healing ammount range difference is increased a little bit. From the values I got, Restoration increased the healing per Heal tile by something like 422~670.
I don’t even know anymore how this sh1t works. Based on these results, you can decide if you want to get another skill in its place.