All true, of course, and the potential for a significant intra-team conflict that affects results for riders on the team negatively is definitely there. But I think that one rider is likely to emerge from the situation as the dominant player, and wind up on the podium, with the most probable position being first. And I think any team takes that, even Ineos.Most of the examples you list are of two teammates competing for the win, not three (you could argue that Astana had four in 2009, but LL crashed out, and more to the point, no one other than Contador was ever going to challenge LA)..
As any physicist knows, the three body problem is far more complicated. If you have two leaders, one of them is usually going to gain separation at a point where the other has to yield and work for him. If you have three, though, you have the possibility of shifting alliances. We got some taste of that from 2009, where Contador in effect was contending against both LA and Klodi, since the latter would have been siding with LA in any conflict with Contador. That probably played into Contador's decision to attack on a key mountain stage, basically knocking Klodi out of contention for second or even third on the GC.
Granted, there was a lot of bad blood between LA and AC that does not appear to be the case with the three Ineos riders, but you also have the wild card situation, where at any point, any two might be fighting vs. the other, the leader. Suppose Bernal takes an early lead,. He wouldn't want either Froome or Thomas sent up the road, because they would be a challenge to him. If one of them did go up the road, I could see the other actually working to let that one go, since it would potentially improve his chances vs. Bernal. And so on. A lot of potential for chaos, it seems to me.
And again, I remind you that Froome in 2018 was less likely bothered by not winning than he would have been in any other year, having just come from an historic Giro win, and knowing how difficult the double would be. If he hadn't ridden the Giro, or worse, finished far out of contention--as had seemed likely for much of the race--I think not winning the TDF would have been a much bigger deal for him. He could afford to be magnanimous to Thomas, because he still had had a great year.