The better takeaway is that on ELF/PIC platforms a call to dynamically linked function is somewhat more expensive than one would assume.
With modern CPU architectures that can prefetch/speculate over indirect jump/call making it comparatively expensive to indirect call in a tight loop (the idea behind PLT is that in contrast to indirect call through GOT it should more clearly signal the intent to the CPU). On the other hand the tight loop is certainly important and this effect will not be so pronounced on any kind of practical code (because of the BTB pressure).
Also, this is interesting observation for various discussions about overhead of late binding ("virtual" in C++) as similar overhead is already there for almost any cross-object function call in PIC dynamic binary.
