Attacking mids don't score goals regularly in the PL unless they are true number 10s like VDV or Bergkamp etc.
Imo he wouldn't be prolific here, 1 in 4-5 he'd probably go at instead of 1 in 2, if anything an Oscar or Eriksen type output would be the best he could hope for
A gun winger would be more likely to be prolific instead in England
A lot easier to be a goal a game midfielder against the likes of Karpaty Lviv and Hoverla Uzhhorod than it is against Stoke and Watford
People said the same thing about Suarez with respect to the 49 goals he scored in 48 games in his final season in the Eredivisie prior to joining Liverpool. If he'd only scored 25-30 goals then that level of scepticism would probably have been warranted, but I think there comes a point where a player is scoring goals at such a phenomenal rate, you have to give credit to them almost regardless of what league they're in.
I wouldn't have thought he'd continue scoring at a goal per game if he moved to England or Germany, but I don't think there's any reason to think a forward with Teixeira's ability would struggle making the step up to a bigger league. I highly doubt he would drop to a goal every 4-5 games though, and I'm not quite sure which alternate reality that prediction is based in?
If you want a more relevant example you need only look at the 4-5 other Shakhtar players who have moved for big money in recent years. Far from struggling, the likes of Douglas Costa, Mkhitaryan, Fernandinho and Willian have flourished in a more competitive environment, and arguably Teixeira has been more impressive than any of them during his time at Shakhtar.