Uh... wait? I just read this and I thoroughly disagree with about everything here on point #1. Saying Magic Casters are at a disadvantage is just false. 100% false.
Earthquake is the de facto best damage ability you can get in the game by miles, and it is a spell. It's cast time is nuts. It's damage is nuts. It's AoE is nuts. And, the cost is easily managable, even at a level 1 base cost of 20. It's so overpowered that I've used it on pretty much every character since the game came out.
I haven't had a chance to test a full explosion radius built yet, but even if Holy Fire/Fireball/etc. are stronger, they would still count as a magic abilities and be #1 in the game. Magic in Din's Legacy is overpowered in it's current iteration. It's not even close.
I think that you have points that would be valid if some of the major other balance issues of the game were addressed, like the lack of level requirements on high-level mail/plate gear and weapons, so you can acquire level 100 gear at as early as level 20. You can even just get a high-leveled piece of gear with like +13 mana regen a second coupled with the in-combat mana regeneration rate passive or a piece of mana gain on hit gear (like +44 at level 100) and boom, who cares about mana anymore? You'll be capped 24/7.
But, since those issues exist, spells are overpowered beyond belief. Hell, even with those big balance issues addressed, they'd probably still be the best because you can use cast speed to speed up spells, but you can't speed up attacks (because weapon speed doesn't effect attack skills cast time).
But, to more specifically address your point on #1, it's already the case that you want to use wands for the best spell damage. They have flat spell damage that is very high, can get cast speed, crushing blow, magic crit and additional spell damage from mods. For example, the wand MageBane (I think) can roll up to 300% spell damage. Good luck getting anything close to that on even a staff!
And, let's not forget that melee fighters have to deal with accuracy and they have an implicit disadvantage for needing to be close to a monster (unless you're using the spell-attack abilities).
Sorry for the rant... but it really needs to be said that spells are anything other than overpowered in the current iteration of the game. I could go on for hours about the balance of melee versus self-cast spells and that's without even getting into summons.
For #2: I actually kind of like the exponential power system that Din's Legacy employs. The difference between a level 90 and level 100 character is great, and that's not something that you see much of in an ARPG. Take Path of Exile for instance. The different between level 90 and 100 in PoE is pretty much negligible aside form a few niche builds. You get a bit more defenses and maybe a couple more minor notables on your tree for 5% damage... No big deal.
In contrast, 90 to 100 in Din's Legacy can effectively triple your damage, move speed, defenses and clear speed simply due to the multiplicative nature of stats. You constantly feel your character power raising in Din's Legacy, until you become obnoxiously powerful in the end game and go around clearing the game at mach speed (https://www.youtube.com/watch?v=Gcgsn7g57W0&t=193s
I also don't think anybody can realistically have issues with the game as is with how you can now use food to get vitality very reliably, and there are options to make the game easier on the area select screen. Though, it's really hard to gauge the difficulty of the game accurately when it is pretty much a faceroll no matter what you do at the moment.
edit: I really wish somebody would call me wrong and tell me Earthquake isn't overpowered so I can show this video of how bugged and overpowered it really is right now.... if only there were more critics