You're talking about two different things: Stock picking and whether dividends are priced in. Because stock picking works for you (let's ignore the sample size issue), doesn't mean dividends aren't priced in.
The reason I believe this is not related to stock picking working for me.
I believe it because the market is not efficient, and dividends being priced in relies on an efficient market. Any success I have in stock picking relies on this inefficiency; it's just a symptom.
I personally value dividend paying stocks more highly than non-dividend paying stocks. A history of dividends makes the stock appear more valuable to me (given that the majority of companies are rubbish at investing in themselves, giving me the money and letting me reinvest it myself is preferable). If they just went ex-dividend, that's a excellent very fresh data point that makes the stock look more valuable to me.
The company has less cash ex-dividend, so as a matter of fact is worth a bit less.
No, but that variation caused by going ex-dividend clearly is.