Taking about a four year cycle on something that has existed for twelve seems the epitome of using too few data points.

GP is presumably talking about the halving of coinbase, ie the mining reward, every 4 years. Currently at 6.25 BTC per Block.

Right, but supply inflation moving from 1.76% per annum to 0.88% per annum is roughly speaking utterly meaningless. People just latched onto this idea because they're using too few data points.

Agreed.

And the idea that miners have a god-given right to make $100 per transaction, $40m per day, and therefore if the mining reward halves, the price of BTC must inevitably double, is obviously preposterous.

You can look up Stock to Flow and Bitcoin to learn more about that theory.