Besides that, I like structured data in the form of an object vs parsing everything from text.
However, this really is more of a unix criticism and less a bash criticism.
But calling bash slow is kind of strange. What are you trying to do in a shell, that you can call it slow? A shell simply parses commands and dispatches them. For example, if you grep a 100GB file and it takes a long time the shell is not the bottleneck.
Why are people approaching a task which has a prerequisite of being speedy with the shell in the first place?
My only complaint about modern shells would be the lack of data structure support. I think it's slowly being remedied what with bash getting basic associative arrays.