Long term and short term work perfectly in normal institutional trading, where one side of the ledger is involved in a longer term trade, and the other side is being run with daytrading traders.
BOTH are methods used by any company working in the business !
while hypothetical at best, the ideas of total diversification as you have stated is recommended for investors, certainly possible and inherently profitable, BUT i look to the original hedge funds which made money because they could SHORT where mutual funds COULD NOT !
had the funds simply stuck to what they did so well and NOT get involved in trading hither and yon, they would not suddenly be bankrupt and while, for an investor, diversification is a good thing as one situation is hedging against another, IF A FUND STICKS TO WHAT IT DOES, be that options, futures, forex or (well, not so sure) equities, it is capable of producing some really startling gains --- its kinda like the jack of all trades vs. the master of one --- will the master earn more ?
I believe you do one thing and do it well and that will work nicely. Of course, if you have seperate departments, all expert, than diversification is a plus, simply because its offering SO MANY MORE opportunities.
me --- im just a one man shop which im happy to remain, so "diversifying" would probably be a death knell !
enjoy and trade well
mp