I'm fine with people playing non-meta supports. I'll give anything a whirl. One of the most enjoyable lanes I've had relatively recently was me as Caitlyn and a random chap/chapet that picked Ekko for support. He would chunk them with Timewinder and then stun them with Parallel Convergence and then dash to them with Phase Dive and proceed to chunk them more with the bonus damage he gets from stacking his passive Z-Drive Resonance. All I had to do was clean-up. Sweet deal if you ask me. XD

Here is the thing though, that despite the fact that Ekko was doing a lot of damage they were playing the role of support and they bought a Sightstone. Sure they could have bought something else to increase their AP and ensure that they picked up more kills. But that wasn't their primary role.

They warded the area around the lane so that we could be really aggro and go ham on the enemy Bot lane. They setup and left the majority of the kills to the ADC who if properly farmed and itemized is going to be the most consistent source of damage output for the your team if the game goes on for any length of time.

Shaco or Teemo may have something that sort of approximates wards with Jack In The Box and Noxious Trap, respectively, but they don't provide 1100-unit radius vision like a Stealth Ward or Vision Ward. You are welcome to use your boxes or your shrooms as a supplement or in addition to wards, but by themselves they aren't sufficient.

We sometimes play with a person that loves to run a utility/movespeed based Teemo as support (don't ask me why). Again, all fine and dandy, except that he refused to buy a Sightstone. After a couple of games of getting stomped because we didn't have the vision we should have we told our Teemo player to buy a damn Sightstone and use it or find another group of people with which to play.

Vision is that important.