Self-serving, but I think sometimes a first hand experience provides a bit of insight in things that could be better.
It's odd to me that the bread-and-butter of all defensive spells, even for a dedicated Abjurer, remains Improved invisibility - which both in terms of duration and damage mitigations provides more than any other accessible spells in EFU's level range.
While the change to the cantrip resistance is a flavorful and a welcomed one, it depreciates in value early on - and the majority of the EFU experience takes place in the range where spells such as II are accessible and in high demand. The classical DnD tradeoff is that Stoneskin is a "morning spell" and Imp. invis one that is used in the midst of combat - but I know that EFU doesn't wish to go that way, for good aesthetic and balance reasons in my opinion.
Why not make the quintessential Stoneskin ward, for dedicated abjurers, a viable if still suboptimal, tradeoff compared with Imp. Invis when it comes to Warding their comrades against physical threat?