SailfishOS is quite efficient. On Sony devices, I experienced maybe 15% extra battery life compared to stock Android, which is quite good given that Sony ROMs are excellent. Sony is known for their Sony Open Devices Program.
I genuinely think if Sony offered a Linux phone and didn't lock it down too bad, they could serve as the catalyst for the whole market. I don't think I would trust any other company at this point to execute the platonic "Linux phone" we need. The uncompromising vision on building a fantastic product for the technically minded make them an obvious choice.
I get the impression they shut it down, but Sony had/have the Xperia Open Devices program. They were close to having their devices running purely on the mainline Linux kernel:
Sony tries out so many different types of products too across their entire lineup. They have made some memorable handhelds over the years, even their eink readers were special.