When swing trading, which I've pretty much always done successfully, I always focused on what I perceived to be the best opportunity at the time. The last time, that was an oil stock which I correctly perceived to be undervalued at the time.
But yes, it might very well be that what you're proposing may be viable.
I just think that specializing may be more relevant when you're day trading since it's in essence about mastering a market.
Swing trading, it's more about recognizing the best opportunity at the time and stalking the market for that great trade and entry.