Wow. Lots of work, and very well done. From what I can gather, many of these issues can be resolved by:
A: Fixing the concentration issue. Larian has always like using terrain effects in combat, and if implemented well, it works. i have found that they have over-done them. This is a fantasy setting. An "Olde Tyme" world so to speak. How the heck do they have so much oil? Biodiesel isn't available yet. Whaling? Well we know how we feel about that.... And drilling for oil? Again, opinions will vary, but how much are they really able to produce by drilling at this time? I 100% agree that firebolt, Ice beam, acid splash and the like should not cause a surface affect. Ice beam is fine slowing down a creature and firebolt does a good deal of damage, plus setting them on fire.
B: Saving throws are made AT THE END of the creatures turn, like in d&d 5e, not at the beginning.
In regards to sleep. As a wizard who would love to relay heavily on this spell, I think one thing that can be done, is have the awake creatures go and be able to "Help" their sleeping compatriots to wake them up (just like in 5e). Also, any damage will wake them up as well, so unless you're one shotting creatures, they will be awake when struck. This way the length of time it lasts can be brought back up.
On this note, I think the Prone condition should follow the 5e rules. You have advantage on the attack (not instant crit) if making a melee attack and disadvantage on ranged attacks (due to the target having a much lower target profile). This should resolve at least some of the Prone condition issues.
Very well done on this list, however.
