Play all songs by the same artist on iOS
Open Music app
Tap (repeatly) on the Library button at bottom left until you get to the top level
Tap on Artists
Select the artist you want
Top row allows to play all titles across all albums at random, tap that
Open the currently playing view
Scroll down a bit and disable shuffle mode


PS: I didn't say it's easy that way but it works well for those artists you haven't defined a Smart Playlist for.