They are not holding back the sport at all. Dropping teams into the top flight just does not work. We have had so many failures of trying to fake teams being top flight teams.
Selection will never surpass sporting achievement.
If Toulouse put on a good show in 2017 I can see the RFL saying that they will expand SL in 2018 to 14 teams. But they need the fans and they need the product on the field.
All those who want expansion regardless of sporting outcomes are blinkered to what most people want to see. People watch sport for the competition not for a rigged system with no consequences.
If Catalan, Toulouse, London, Canada and Wrexham were all dropped into SL in 2018 and told they would face no possibility of relegation at the expense of say, Hull KR, Huddersfield, Widnes, Leigh and Wakefield I think it would basically draw up the bridge again, numbers watching would drop and quite frankly fans would get bored as there would be no competition. Just several rounds of meaningless games.
With the current set up, teams can grow like all other sporting teams in the UK.
With some RL expansionists in charge of the Premier league there would have been no Leicester City phenomenon.
They would have been so appalled that a small team could do so well they would probably remove them from the competition mid-way through the season.