Are you sure you don't empty @ARGV before trying to use it in the sub? What you say doesn't appear to be true.

>perl -E"Foo::foo(); package Foo; sub foo { say for @ARGV }" a b c
a
b
c
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@ARGV is global, even using it's unqualified name. You could also use its fully qualified name, but it's not necessary.

>perl -E"Foo::foo(); package Foo; sub foo { say for @::ARGV }" a b c
a
b
c
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@::ARGV is also known as @main::ARGV.