You keep using that word ("syntax"). I do not think it means what you think it means.
Syntax, as far as I know (and I am no linguist) is the arrangement of "words" into "sentences" as described by or conforming to a grammer. When I say "perl's OO syntax", I mean the various keywords/operators in perl that when combined in a certain way, create OO perl code. What do you think I am meaning when I say "syntax"? Please explain, or correct me if I am wrong in my thinking.
As for use base, yes you can look at it as a keyword with a space in it, but that does not make it a keyword. If you were stuck on a desert island with just an interpreter and no modules, you would have to revert to the ugly @ISA = qw(Bar); form (although I suspsect you would likely just implement your own base pragma).
Please note as well that I make my living writing OO perl code and enjoy I enjoy doing it very much. But having to work with it every day has convinced me that there is room for improvement.