Devils Advocate here - I'll preface by saying I agree that Clairvoyance needs a change (or just removed) but there is a problem with your logic because it ignores several variables.
Which champions like Blue trinket? ADCs, Xerath, and Nocturne.
ADCs are in a duo lane where heal is the meta because it heals both champions and gives a movement speed boost for safety.
Xerath functions well with a large number of summoner spells, including ghost, heal, barrier, exhaust, and even ignite. Vision isn't really important to him until he gets his ult, and oftentimes summoner spells dictate lane phase before level 6. Ghost, ignite, heal, exhaust, barrier, and ignite could save his life or get him a kill before level 6 so they're all more valuable than the vision summoner.
Nocturne is generally played in the jungle, where smite is a requirement. So Nocturne simply can't use Clairvoyance.
Flash is also generally considered a requirement for all of the above champions, which is why I left the second summoner spell option closed.
So based on the above, unless Clairvoyance gives combat stats or enhances mobility somehow, then it will never be used over flash or a combat-based summoner. It doesn't matter how much you buff it, because the other summoners will always be better by nature.