But in that clip above Gareth specifically says we are only allowed 21, whereas the Aussie teams are 23+23
What he says isn't true - we have 23 contracted players this year (not including injury replacements), and the NYL teams are a maximum of 16 players.
However the Aussie teams are allowed to add 3 of their NYL players to their roster, effectively giving them a possible 26 man roster. That in itself isn't really much of a disadvantage for us. It's not having a reserve/youth team that is more of a problem, although in a weird way there may be a small upside in not having an NYL team because we are able to bring in any player we want as a replacement player whereas except in exceptional circumstances (supposedly!) the Aussie teams have to promote a youth player.