I mean Gatha fucking around in Kheld is what tipped off the Phyrexians to the Bloodlines Project and got the "Hero Bloodlines" outside of Crovax, Sissay and Gerrard killed..and got Crovax corrupted.
It also delivered a ton of research to Urza when Gatha died, research Urza couldn't conduct himself with who he had. The Gathans were also a major pain to Phyrexia and essentially consumed their attention completely and forced them to expose a lot of what Rath was just to keep up with the Gathan Kelds.
Yes he was doing something semi important, but Yawgmoth was planning on Abandoning Phyrexia anyways IIRC.
Kind of, Yawgmoth was going to go back to Dominaria where he originated but he still planned to have Phyrexia and if the bombs went off when they were planned to Yawgmoth would still be on the plane when it collapsed.
That was less a fail safe and more..Urza knowing that Szat was gonna fuck around and find out.
It was both, Szat wasn't the only one with the kill switch, he was just the one he expected to fuck up and be used as fuel for the bombs.
I am not saying Urza did nothing for the Coalition but they certainly are still an effective force even with him dead..Ironically largely because of his descendant Jodah (Jodah is Urza's great..great grand son I think? I think he recalls his Grandfather talking about his Grandmother Kalya)
Sure, the Coalition was more than Urza, and Urza was aware of that which is why he gathered the people he did. As for Jodah, he is related to Urza a few generations down the line and in Ice Age he remembers the ancestral home built by Kayla's son, but he isn't fully aware of his lineage. He didn't really play a part in the Coalition originally, and remember, Barren, the first breeding experiment of Urza was the father of Hannah. That's not to say Urza planned everything down to the last detail, but he had a hand in most things that happened to take off on their own, even something like the Shivan Rig standing up and functioning as a walking battle titan was a surprised to a lot of people working on it.
I think that's what made the old story so enjoyable, it was very much dictated by the top dogs like Urza and Yawgmoth, but the people under them had autonomy and their decisions were important even if they were pointed in the right direction by the hand of their gods. It's realistic in the sense that the higher ups create the overall battleplan and organization, but the ground commanders execute it, and if either is fucked it all collapses. The modern story is that none of the ground commanders matter and it's a couple people doing everything.