It's a tiny bit more scriptable, but it's not like a real API either.
For instance, I remapped the backtick key since I rarely use it.
' | means split vertical
' space means split horizontal
' h,k,j,l means go to the left down up right pane.
' z means zoom the frame to full size
If you are interested I can show you my tmux conf. I'm not a ricer, the config I use is very simple, I find it just removes friction and makes it much more usable. Plus I can still type a backtick by pressing it twice
How is it less capable?
With screen, I can have windows 0 and 1 in a vertical split on my laptop, and windows 0 and 3 in a horizontal split on my desktop.
With tmux, you attach to a session and it has the same layout everywhere. You can have attach different servers or different sessions but you can't even show different windows in the same session, let alone have different layouts. If my laptop shows window 1 containing 2 panes, my desktop can only show window 1, and it will contain 2 panes. Changing the layout or the active window will change it everywhere.
I simply deplore that the tmux developers obviously thought long and hard about this design only to come up with something needlessly complicated and in the end less capable than screen's model (since you can't have different clients with the same windows in different layouts).