Is there more efficient way to use the usb c ports for external display on macbookpro?
Your monitor supports daisy chaining over displayport 1.2
According to the manual you can connect the two displays together and then use only one cable to your device. (page 26/71)
Note that your graphics card must support it as stated on the page:


  NOTE: U2413/U2713H support the DP MST feature. To make use of this feature, your PC Graphics Card must be certified to DP1.2 with MST option.


I dont believe apple enables these options though, I found this answer on this site which also states that it does not work in osx Sierra.
You could always try and see if high Sierra makes a difference.