The future selves that the Time Lords can perceive and summon are not the future selves that Lin Yuan cultivated through the "Three Lives Technique".
The latter is based on the current and past selves, condensed from marks on multiple future timelines, while the former... is the true and undistorted future.
Whether or not one has cultivated the "Three Lives Technique" and become a Time Lord.
The future indeed exists; it's just undetectable and uncallable below the Time Lord level.
A time life being can observe future timelines, but that doesn't mean they can communicate with their future self.
"The Blood Sea Lord is actually summoning his future self?"
"Could it be that the future self the Blood Sea Lord senses has already taken that step?"
The Time Lords watching around had serious expressions. Normally, summoning a future self is not very significant for a Lord.
