I agree that trend analysis has a lot smaller foundation for the long term, but in the short run its essentially analyzing the supply and demand of the stock, which can be predicted (not all of the time of course).

Outside factors like news don't occur everyday, so the using technical analysis for intraday trading is very reasonable

Then you better not buy index funds. Those are basically trend-following systems over the long term.

And there is statistical data to back up that trend following does work.

regardless of whether it has "theoretical basis", there are plenty of hedge funds that make plenty of money with it.