Shouldn't a level 20 Abjurer's ward be 45 HP? 2 x wizard level + INT. Or did you mean to say level 10?
Good catch, I'll make an edit. I meant level 10.
War Magic's Power Surge seems worse than Evocation's Potent Cantrip, IMHO (and that's saying something, as much as I love Evocation). Unless you're fighting casters, you can only use it once per short rest. So for a level 6 War Mage, that's 3 damage per fight, assuming you get a short rest between them. Potent Cantrip will net you approximately 3 damage every time you miss with Frostbite at that level (more for Toll the Dead, but let's keep the numbers low to be conservative). In my experience the real benefit of Potent Cantrip is psychological quality of life. With it, using an appropriate cantrip means you can never have a turn where you contribute nothing. Your average Frostbite damage at that level vs an orc only goes from 3.2 to 4.8 (Empowered Evocation hasn't kicked in), but in two misses you've caught up to the War Mage in terms of extra damage.
To some extent, it seems like a disagreement over which tastes worse, lima beans or liver. They are both bad. The reason I think Power Surge is a slight bit better is flexibility. Potent Cantrip is only providing damage if we assume that:
1: You are casting a save or take damage cantrip in combat
2: The enemy fails their save
3: This happens multiple times per short rest
Even then, which battles are you casting cantrips? I expect the easy battles. These are the battles where that damage is less important. When is the War Mage using power surge? I imagine vs the big tough baddie, where more damage is important.
Also, as we go up from level 6, we would expect to use less and less cantrips in battle (eventually we use none, or near none). Power surge on the other hand, will increase in damage as we go up in level, and we will always be able to use it.
Still, they both are pretty bad. Lima beans are worse though.
I would actually be very interested to hear how your (or anyone's) experience with the War Mage went. I can't seem to get past the idea that the Arcane Deflection shuts down your ability to use non-cantrip spells until the end of your next turn. You say it's not much of a handicap at all, but this is a far heftier cost than that of a Bonus Action spell. Depending on where in the turn order you used it, the battlefield could change a lot between when you used Arcane Deflection and your turn. You might not know you're about to be swarmed and in need of Misty Step. Or you get attacked again and wish you'd used Shield the first time, but now you don't have the option. I don't know, this one just makes me nervous.
I think Arcane Deflection is a great combat ability at low level. I'm not using counterspell at that point, and if I can save a spell slot (that shield would use, or absorb elements would use) then that's quite valuable. In addition, I might be out of spell slots entirely, in which case, this is a gift that keeps giving, with no downside at that point.
As levels increase, I think it becomes more and more a non-combat ability. Hit by a poison dart trap? Arcane deflection for +4 to poison save. That kind of thing. My 20th level wizard would never use this in combat....I don't cast cantrips at that level much at all, and being restricted to cantrips is not worth it.
