Only once in 15 years have Panthers averaged over 14k at home and that was in 2018. Despite success we have higer attendances on average because we choose a right groud right games strategy. So seems that your argument actually supports not going back .
Manly despite lots of winning years only scraped over 14k at brookvale in 2008 and not since
Wests tigers in the same period have regularily averaged over 15k and quite often over 17k ave home crowds despite being rubbish.
Our residency at ANZ and Parra Stadium would definitely be contributing to that average.
Since 2015 (abitrary date selection as it gives us five seasons until 2020 when COVID ruined everything,) this is how many games above 15K we've had at our respective regular home grounds:
Leichhardt Oval
2015 - 0, average 10.5K (4 games)
2016 - 1, average 13.3K (4 games)
2017 - 0, average 12.1K (4 games)
2018 - 2, average 16.1K (3 games)
2019 - 1, average 14.2K (3 games)
Campbelltown Stadium
2015 - 0, average 9.4K (4 games)
2016 - 1, average 12.3K (4 games)
2017 - 0, average 9.6K (4 games)
2018 - 0, average 9.4K (3 games)
2019 - 1, average 12.0K (3 games)
Stadium Australia & Parra Stadium
2015 - 7, average 19.4K (8 games)
2016 - 4, average 17.3K (8 games)
2017 - 4, average 19.1K (7 games)
2018 - 5, average 18.9K (7 games)
2019 - 3, average 16.7K (7 games)
Overall LO does better than CSS, but we only have seen 2 more games above 15K at LO than CSS, and only one season where either spiritual ground saw above 15K. Stadium Australia and Parra Stadium seriously pads our ground averages and is the only ground(s) where we average above 15K yearly. Our surburban grounds don't attract like the bigger stadiums, and that's probably because the opposition are turning up in droves to watch their team spank us.