When Stadium was the standard RBY metagame on PO many moons ago (on the order of 1000 battles played per month), Jolteon saw 10-20% use as the main abuser of Focus Energy (
http://stats.pokemon-online.eu/past-stats/). Its usage grew from 10% in January 2012 to 15-20% by June 2012. Its usage seems like it was even higher in the ranked stats (which frankly are the stats that matter - oops for not reporting those instead!). Once cart-RBY was implemented, Jolteon usage fell to 5% by January 2013 (and less than 3% in the ranked stats). Note that Jolteon usage seems to have remained high for some time in between, presumably because people were still trying to use their Stadium teams in cart-RBY.
All this is to say that a fixed Focus Energy not only
should, but
has yielded increased Jolteon usage. Moreover, this increased Jolteon usage was likely a stable strategy and not just "new toy syndrome", as Jolteon usage steadily crept up, rather than skyrocketing and crashing down to earth, during Stadium's tenure as PO's only form of RBY (the "crash", recall, came because PO finally implemented cart-RBY between June and July 2012).
Other focus energy users, as far as I can tell, were not used nearly as often as Jolteon. So "fix focus energy", for all intents and purposes, is probably a Jolteon-exclusive effect, metagame-wise.
Of course, that was a different era of RBY, one before correct Body Slam mechanics were discovered, when Egg was a mandatory team member, when Golem often saw more usage than Rhydon, when people actually used Slowbro, when I was still in college, and when Jolteon was much more of a novelty in cart-RBY than it is now (this SPL, it was used in roughly 13% of teams even without a functioning Focus Energy, rivaling the Stadium usage I just mentioned). So it's unclear how well these data would translate to RBY as she is played today.
