Firstly, who gives a f**k what a Swans chairman's opinion is. Whether or not he's another dumb merkin that doesn't understand the difference between correlation and causation is irrelevant to the discussion.
Secondly, "relative lack of growth since"! The f**k are you talking about!
For simplicities sake we'll just look at members-
The Swans had 3,327 members in 1994.
1995- 6,088.
1996- 9,525.
1997- 22,109.
Jumping ahead to today (2022) they have 51,642, however they had their highest membership numbers in 2019 (pre-covid) with 61,912 members.
http://www.footyindustry.com/?page_id=228
Almost all their metrics see pretty consistent growth from the early 90s to 2019, with the exception of a few spurts after GF appearances in the late 90s, mid 00s, and early to mid 10s.
The sole exception to that pattern of consistent growth is their crowds, that have been pretty up and down since 1997, but also follow a pattern of their competitiveness on the field.
TL;DR- it's utter nonsense to suggest that the Swans growth stagnated after the SL war.
Firstly, Super Rugby's peak in Australia was 96-04. So they didn't have a great deal of time to do much growing after SL before SR started to decline did they...
Secondly, Super Rugby and the A-league's successes and failures can easily be patterned by decisions they made within their own games. As such it's not necessary to add in unprovable airy-fairy nonsense like "they were only successful because of SL", so why attempt to force that factor to fit when Occam's Razor would suggest that it's not the case.
Furthermore, the A-league didn't see any real mainstream success until 2014, and SR didn't start to totally collapse until the mid 2010s either, by which time RL had already been well on the road to recovering from SL for a decade. So your assertion doesn't even make sense on that level.