I don't disagree what you're trying to say but your interpretation is a bit weird.
If we're talking about about overheads (aka expenses), we have to consider all revenue in general, and consider that some revenue goes to a club directly, not via NRL/AFL head office revenue (for example, buying a beanie from the club website as part of overall merchandising revenue and expenses for both sports.
AFL makes far more revenue outside of its non-media rights package. More sponsorships, more memberships, more corporate, more ticketing, more merchandising for the clubs. Less fees from gambling, though, granted. That's outside media rights too.
The AFL doesn't just 'prop up' GWS/Suns via revenue raised in media rights. It does so from the overall package. AFL has been able to decrease their variable funding to the Brisbane Lions in recent years, as they have bigger attendances upon winning premierships. That's a bigger pool of money the AFL has to be able to prop up the deadweights of GWS/Suns.
And in any case, I don't see how you can interpret the NRL's decisions to spend on non-core spending outside of its competition - like super league and internationals - as "accelerating growth" - as being any different to the AFL's logic as to why it has a deadweight in GWS/Suns in the first place. To be clear, I'm not saying the these clubs are not deadweights, I agree with you on that. It's just that the same logic applies as to why the AFL brought them in - "accelerating growth, come new media deal more money". Those two teams lose money, but they brought indirect benefits to the AFL with a greater, consistent presence among all 5 major markets + Canberra via GWS to an extent (AFL was only playing 1 game a year in Canberra before GWS, not 3). Who knows how less money Toyota would pay for national sponsorships for example, now that the AFL can trick Toyota in telling them that their competition is "truly national", and their logo is plastered in every city every week? The NRL can't go to its national sponsors and claim that it's a "national brand" in the same sense that there are not games in Melbourne, Adelaide or Perth every week. It's stupid, I agree, but having worked in this industry before, the companies that might pay the millions of dollars for these types of sponsorships care about this BS stuff.