In G&K, Artillery is now available earlier, contemporary with Riflemen and Great War Infantry, and is very weak against Atomic era (WWII) Infantry. And there isn't another siege upgrade until Rocket Artillery, which really shouldn't be available until the Information era. So it would be nice if they added a new gunpowder siege unit somewhere and reshuffled the rest, as they seem off now. Either a new early 1500's cannon that's strictly a siege weapon (and push back Cannon and Artillery), or a new 1890's howitzer-type weapon and push Artillery back to Atomic era and Rocket Artillery to Information era.
It's true that bombers supplement artillery starting in the modern era, but they're somewhat limited in functionality, and dependent on Oil.