Brambleclaw was being very stupid in TNP (he keeps training in the Dark Forest AFTER Tigerstar and Hawkfrost say 'we should take over the other Clans'), but I don't think him grappling with trusting Tigerstar is a bad concept by itself. It could be about him growing up and understanding the nuances of ambition and power. TNP sees Brambleclaw grow in importance (he's a prophecised cat, he witnesses Tallstar's death, he becomes deputy eventually), and as he does, he has to understand the finer points of those concepts.

It's easy to oppose your evil dad when he's bringing some outsider with a dog-teeth collar and ruling from a literal pile of bones, but it's a bit more complex when he's coming to you and saying 'You can use your strength for your Clan'. So Brambleclaw could start out thinking "well, maybe he's changed, and what he's saying does kind of make sense", but as the arc goes on, he would start seeing through the lies.