According to Bass & Walleye Boats magazine, it appears Mercury may have detuned the 200 EFI in 1997, 98 or 99. Bass & Walleye Boats had a 200 shootout (a competition among engines) in the April 1996 issue with Merc, Yamaha and Evinrude running their 200's on identical Champion 191 bass boats. Mercury took top speed honors by 1.1 mph and had the fastest 0 - 30 mph and 30 - 50 mph acceleration times. On the dyno the Merc showed 206 hp, the Yamaha 204 hp and the Evinrude 199 hp.
The magazine had another 200 shootout in 1999 where the Merc 200 EFI had a poor showing. They tested 7 engines total, 2.5 liter carb and EFI Merc's and a 3.0 liter Opti, 2.6 liter carb and 3.1 liter EFI from Yamaha and 3.0 liter carb Johnson and 3.0 liter 200 Ficht Rude. The Merc 200 EFI top speed was just below middle of the pack, 2.4 mph slower than the Evinrude, and acceleration times were the worst of all the engines. Bass & Walleye Boats actually specifically said in the article the Merc 200 EFI was a big disappointment compared with 3 years earlier when it took top honors in all categories.
I ran in bass boat circles back then and the word going around was that Merc detuned the 200 EFI because they were just trying to pull too much out of just a 2.5 liter engine, smaller than OMC's or Yamaha's blocks, and there were reliability problems and to control warranty costs. There is a Scream & Fly post from February 2013 that says Merc detuned the 2.5 liter 200's in the late 90's to try to steer people to the Optimax, and to give customers the feeling that they were getting something for their extra money buying the Opti.
Does anyone know if Mercury changed something to lower the power output of the 200 EFI sometime in the late 1990's? In readers' experience running 200 EFI's or hearing from other boat owners, does anyone get the feeling that late 90's 200 EFI's develop less power than the earlier ones?