My two cents worth!
Barzini tried to car bomb Michael, whose surviving was pure luck as well, same as the others and to keep the plot moving

I reckon, he couldn't finish them off because of the peace deal but no doubt underestimated Michael and overestimated their perceived weakness, when Barzini's people chisel Tessio's territory, and they did nothing about it

Fredo telling Mike about Questadt was not what ended up saving Mike's ass Small potatoes!
It was Frankie's brother's presence who was already on his way so I reckon Mike going to jail was never likely

What is the point of having a better plan and over three hundred million dollars when no country would take him -- not for a million -- not for ten million. Then end up killed, at an airport

while he lost two of his capos, his brother, his marriage, he didn't end up dead like Roth In fact, as we debated in Did Roth sort of win? thread:
1. Roth was a formidable enemy but let's not overstate the impact he had on Michael
2. he was richer, more powerful and "legitimate" than ever and there were happy times in GFIII

Don't know Pete, I reckon, attack on the Top Don, wouldn't have been without Barzini's backing and sanctioned by him
Tattaglia is a pimp and as Lou posted, the Fredo of the Commission