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.
You and jod want goals though, 1 in 4-5 games is extremely realistic in the PL
Teixeira is not what I would consider a forward, he is an attacking mid, I consider Firminho an attacking mid also, but I see he's played upfront the last week, he could be converted perhaps
I wouldn't bother quoting the likes of Fernandinho as he's a holding mid, while Costa and Mkhitaryan play for the top teams in a vastly weaker league
Suarez is a striker who floats on the wing or at number 10 when he's not playing at number 9, Alexis Sanchez is similar in playing style when he plays upfront occasionally imo, those types of players generally do well in the PL, see Ronaldo, Mahrez, Bale also etc and Walcott has been prolific at times also.
Top attacking mids in the league, minimum requirement 50 PL apps (or close enough)
Ozil: 68 apps 12 gls, 1 in every 5 and a half games
Cazorla: 120 apps 23 gls, similar rate to Ozil
Oscar: 112 apps 21 gls, 1 in every 5 and a half
Barkley: 98 apps 14 gls, 1 in every 7
Lallana: 114 apps 18 gls, 1 in every 6.33
Coutinho: 98 apps 18 gls, 1 in every 5.4
Silva: 177 apps 35 gls, just over 1 in every 5
Nasri: 209 apps 35 gls, worse than Silva surprisingly
Mata: 150 apps, 37 gls, 1 in just over every 4, numbers were much better previously
Sigurdsson: 131 apps, 27 gls, 1 in every 4.85
Lamela: 64 apps, 5 gls, lol
Eriksen: 83 apps, 21 gls, just under 1 in every 4
Sessegnon: 152 apps, 24 gls, 1 in every 6.33
Top wingers/wide forwards in the league
Walcott, 224 apps, 53 gls, 1 in every 4.22
Sanchez, 48 apps, 22 gls, 1 in just over every 2
Willian: 82 apps, 9 gls, 1 in every 9
Hazard: 126 apps, 37 gls, 1 in every 3.4, numbers were way better before this season
Bolasie: 79 apps, 8 gls, 1 in just under every 10
Mirallas: 101 apps, 23 gls, 1 in just over every 4
Lennon: 292 apps, 28 gls, 1 in ever 10 and a half
Mahrez: 71 apps, 20 goals, 1 in every 3 and a half
Sterling: 116 apps, 23 gls, 1 in just over every 5
Navas: 86 apps, 4 gls, lol
Young (before being converted into a full back in 2014): 241 apps, 41 gls, 1 in every 5.87
Mane: 50 apps, 13 gls, 1 in just under every 4
Tadic: 52 apps, 10 gls, 1 in every 5.2
Arnautovic: 81 apps, 12 gls, 1 in every 6.75
Chadli: 74 apps, 14 gls, 1 in every 5.28
Brunt: 206 apps, 22 gls, 1 in just over every 9
Alexis Sanchez is the most prolific "midfielder" in the league, with Hazard, Mahrez, Mane, other wing-wing forwards behind him. Eriksen is the most prolific attacking mid, with Mata and surprisingly Sigurdsson behind him
Teixeira will not score at a prolific rate in the league, look at all those numbers he's up against, if he did he'd be the best player in the league pretty much. This league is built for strikers/wingers/pure number 10s. They are the most likely to be prolific scorers in the league imo.