Diego Costa went from #1 option on league winner in La Liga to #1 option in league winner in EPL, and scored at basically the same rate / appearance. EPL also averages more goals per game than La Liga. There really is no evidence to say its easier to score in La Liga than EPL.

Diego Costa was #1 option on both teams, and scored at basically the same rate per appearance.

If you look at the last 2-3 years of forward transfers between EPL/La Liga, forwards generally havent found it much harder to score in EPL than La Liga. Suarez scored more per appearance in EPL than after he switched, Sanchez scored more per appearance in EPL than in La Liga, Bale scored more per appearance in EPL…