It doesn't matter if that would be the extreme edge case. It's a case that CG needs to consider when making a change like this.
Just because you don't like their final decision doesn't mean that they didn't consider the extreme edge cases. I mean, if we're just talking about what's possible without actually caring about the data you dismissed (about 44k TCs in the game), then it's possible that there's a guild with 50 players who have 0 Sidious shards.
That would make as much sense as a guild playing ROTE with 0 shards of TC among its 50 players.
Again, no one is saying that it's impossible for one guild to be hurt more than another by this choice. But a different guild could be hurt more by choosing Sidious than by choosing TC. I mean it's POSSIBLE. So why care about data?
If you have 3 g12s out of 50 players, then **at most** you're going to miss 6/6 one time because of this change -- at least if you care about filling platoons and everyone is chipping in for guild success.
Statistically there are enough guilds that someone's TB officer is going to fail to coordinate the switch because they get in a car wreck or go through chemo or lose to the Patriots or some other catastrophe that seems impossible to happen in the next week to folks living their daily lives. Will some guild miss 6/6 because of this? Sure. You have enough guilds something is going to go wacky in a few of them.
But unlike you, I think that CG did look at the data and did consider the effects of choosing Chieftan. They just made a decision that you don't like.
I'm still crossing my fingers that your alliance guilds who were getting 6/6 before will get 6/6 again. But if they don't, 2x Raid is enough to go from zero mats to 40 ECs and 10 Zinbiddles. That takes at most 1.5 weeks. The other resources are likewise available in 1.5 weeks. If a 6/6 guild misses it this time, they'll make it the time after.