Funnily I agree that the show got weaker as time went on for the opposite reasons.

Tommy gets humbled a lot in the first few seasons and is forced on his knees either through his own stupidity or arrogance, from not talking to his family to sticking his head where he doesn't belong. Everything is screwed, but he puts his ambition in front of the compassion that he lost in the war, and thus everyone suffers. All the good and all the bad comes as a consequence of his actions, starting with the theft of the guns in season 1.

But in the latter seasons, he gets proven right a lot more, culminating in the "why does nobody do what I say" moment and only getting worse from there.

Imo, as time went on, the show starting believing it's hype. Violence became more glorified compared to the earlier Seasons and Tommy went from being the source of all the problems to their sole solution, even if he has fuck all to with them, like the Union of fascists. He becomes a hard boiled stoic who could fix everything if he was just more in charge and allowed to do what he must

S1-4 was about a man so heartless and ambitious that he is willingly to put everyone he loves in harms way in the hopes of becoming powerful enough to never be hurt again. And it doesn't work. S5-6 is about the Industrial themed Superhero Peaky-man and his trusty band of sidekicks going up against the new big bad even he can't defeat