Tony called the hit off only after Carmine unexpectedly decided to compromise and meet Tony's demands. Those blacks that Chrissy knew already had clear instructions how to take out Carmine, it was a matter of days. Besides, conspiring to kill a boss is a major thing that doesn't just go away like that as if nothing ever happened, Johnny himself reminded Tony of that ("The thing is, we had those conversations. Your mouth was moving along with mine").

As for Rusty... Indeed by keeping Johnny happy Tony thought Phil would be controlled. But Johnny's power was clearly fading at that point and he was facing 15 years in jail minimum. By killing Rusty, Tony potentially made a lot of enemies in that family, if it ever came out that he was behind it, and it didn't really win him much sympathy from Johnny's/Phil's faction.

Remember when at that sitdown in the last episode Tony accused the deceased Johnny Sack of creating constant tensions between the two families, but in reality it was actually him who was doing that since 4th season or so. At least, I see it this way.

All in all, it wasn't wise from Tony to get so much involved in NY problems and it ultimately backfired. Of course though, it's a show and it made the plot interesting so I have no problems with it.

Making Junior a lighting rod IMO wasn't a good decision. It's not like Chin-Salerno situation because Juniors didn't know about this arrangement and it naturally made him very angry when he found out. It sparked a war and Tony was lucky not to be killed because of it.

Tony was good at recognizing rats though and had some charisma. I don't agree that he was "the worst" boss ever depicted neither it's just that Sopranos are by far the most famous TV depiction of the modern LCN which is in decline, so it's natural we won't see a 'Michael Corleone' or something.