Perl allows optional delims if ambigious. so if the best set <> is ambigious double or triple them. But much easier would be to demand uppercase T type variables.

   a, b = w < x, y > (z)

w is lowercase, unambigious. Parsed as list of comparisons.

  a, b = T < x, y > (z)

Ambigious, so use

  a, b = T <<< x, y >>> (z)

instead. These cases are very rare. Or demand parens for such ambigious lists of comparisons. Might be too late already.

Of just demand the type keyword there also:

  a, b = w < type x, y > (z)