Why do inductors shift current by the same amount?

[iScience]

phasor diagrams: what happens @ R=0?

when R=0 and there is only the inductive impedance, what's the angle?

 

[Simon Bridge]

when R=0 and there is only the inductive impedance, what's the angle?

... have you tried looking it up?
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/phase.html
https://www.physicsforums.com/showthread.php?t=598543