The thing is - when you compare Gerbera before and after blooming, the art style is eye piercingly different from what it used to be. Has nothing to do with artist getting "better". Thats a complete shift from what made Gerbera unique in her own right (the, by some called "eerie" smile and slightly rougher, less "sparkle sparkle shiny shiny mahou shoujo chan desu! visuals).
The reason we suspect a different artist for it is simply, that its starnge for an artist to give in the pressure of the masses and change the way his girl looks by 180 degrees. Its like when a writer who specializes in Romance genre, would suddenly be made to write a horror story - against his own better judgement (as in: if he doesnt want to). And also since you know artists - they dont usually let people dictate how their creativity should take form.
Rather its suspected that its a completely different person who did her Bloomed art.
Granted this is purely our speculation, however the points I gave are making for a pretty solid base reasoning behind it.