Indeed, cards are too intrinsic to AoE3 to simply cut out.
I think if budget were not an issue (a big ask, of course), one possible way to make AoE3 more accessible is to borrow from 2010s design trends and add draft and/or roguelike modes similar to Arena in Hearthstone, where players have to choose between randomly given options to build their decks, either before a match or during one.
If done right, such modes might ease players into learning the game, rather than frontloading the work.
I wrote a bit more about the pre-match version: