It's true, but I have never seen Sky/Ineos have a goal of maximizing their chances in three GTs. They, more than any other team, have coldly embodied the realization that the Tour is 90% of the attention and money in cycling, and have thrown everything at it since their inception essentially.
The only times I can remember them even moderately hyping a tilt at a GT other than the tour:
- Wiggins Vuelta 2011 after he crashed out of the Tour and before they'd really won anything as a team
- Wiggins Giro 2013 after he had won the Tour and wanted to go for the Giro for a lark, plus it was convenient to avoid the blatant obviousness of Froome being better
- Porte in the Giro for a few years where he wasn't good enough to win the Tour, but wanted to lead and was good enough to get his own camper van
- Thomas in the Giro for a couple of years before he had really done anything in GTs and needed a proving ground (which mostly proved he could crash out of races)
- Froome in the Vuelta because he wanted to eventually complete the set but didn't want to gamble on doing a GT before the Tour without a 5 week window (several times)
- Bernal in the Giro because they didn't want a leadership controversy (and then he broke his collarbone and they did anyway)
They never really hyped (or, at least in my perception) the GT attempts of the likes of Landa and Henao.
The whole 'Thomas and Froome can focus on the other GTs' is just saving face. They throw all their best power at the Tour, and Jumbo putting together a train that is better than theirs scares them. It doesn't matter if Carapaz wanted to peak for the Giro, they'd rather have him super-dom for Bernal and give Bernal a better chance at not being worked over by TJV than win the Giro with him. Carapaz, Sivakov, and even Castro and Kwiatko are showing better climbing form than Froome and Thomas, so they got picked. I think leadership of the other GTs is an afterthought, and if they choose to spin the focus on that, it is reverse engineering their motivation.