Is it true that ($match){1}+ equals to simply $match? Yes, and the + does nothing here, as you can see with use warnings:

That's only true because you the OP included a quantifier in the embedded regex; and you get 3 fails because your anchors guarantee the regex used couldn't succeed (which doesn't seem like a useful test?)

This shows that {n}+ is a valid quantifier:

use strict;
use warnings;

chomp(my $match = <DATA>);
chomp(   $_     = <DATA>);

for my $regex (
                  "($match){1}+",
                  "($match){1}",
                  "($match)",
                  "($match)+",
                  "($match)+?",
              )
{
    print qw(FAIL SUCCESS)[ !! m/$regex/ ], "\n"
}

__DATA__
(?:a|b)
bbab
[download]

C:\test>junk37
SUCCESS
SUCCESS
SUCCESS
SUCCESS
SUCCESS
[download]