As someone who actually watches the juniors but also hates the culture of the club & fans pandering to mediocre local kids, I think I have a pretty balanced perspective on it.
Highly rated juniors fail all the time, the idea of trading one isn't necessarily a bad thing and there's plenty of juniors currently at the club who I wouldn't have blinked at losing. Bradbury was above that line for me, but more specifically trading him for a player I believe would substantially improve our chances of success would be one thing, doing it for a completely unproven depth player who'll be in his 30's mid-way through the deal is shortsighted at best. The rugby 7's backstory is nice for the media to write about but the facts are he's in his late 20's with 7 NRL games to his name, multiple of which haven't even been at fullback, and all of which have been filling in behind a well-coached team rolling up the top of the ladder.
When the rumour first popped up the idea of him being a stopgap for a year was fine with me. Probably wouldn't magically make us a team that matters towards the end of the season but the attack should be more exciting and him combining with Dom & maybe Marzhew on kick returns should create some highlights. The consensus on here seemed to be that he would be keeping the seat warm for Pryce in 2024 or maybe even Hodgson sooner. Giving him a 3-year deal indicates that's not how the current decision makers are viewing it, and I don't know what I'm less excited about; the idea of making this trade for a stopgap depth player or the idea of Miller still being the plan for beyond this season. It doesn't fill me with excitement for our next few years to put it nicely.
Not to mention the club putting itself in the position where they need to make a trade like this a month out from the season. It's awful management no matter how you slice it or how much you believe in Miller.
TL;DR: more of an issue with what we got back than what we traded away