I really can't answer that question. I'm pretty sure Barca would play a different style with van Persie instead of Messi. I think he's capable of scoring 30-40 goals in a dominating team, but I don't think Barca would be similar dominating without Messi. Like I said before, you make it sound like 40+ isn't very special. Falcao scored 24 goals last season. Villa never had 30 goals a season, if I remember correctly. Aguero never more than 20 in La Liga. C. Ronaldo only scored 26 in his first season, 40 in his second. Van Persie must help the team to play equally dominating like Ronaldo and Messi do and then score like these two in their best ever seasons. So 40+ is a huge stretch, it means to equal record breaking seasons of all time greats.
I used Huntelaar because Schalke played Arsenal this season in the champions league and I thought both teams aren't far apart in quality overall and both finished on similar positions in their respective league last season. I don't think there's much between Bundesliga and Premier League in quality overall. Developments in european competitions point in that direction, as do results between german and english teams in recent years. Teams like Malaga (54 goals last season) and Atletico (53 goals last season) score overall way less goals in the league than comparable teams in England like Arsenal or Tottenham, so I don't believe it's easy to score these amounts of goals in La Liga for top teams with great attacking players. I don't get the wage bill comment, always thought it's about the squad's quality not about how much a player gets paid.
More importantly I used Huntelaar because as a pure goal scorer he is not far off RVP. Van Persie is overall a way better player though because he's able to create for himself, he's technically far more gifted and a better team player. All those things lead to him helping his team score more goals than the same team with Huntelaar upfront would do. So Huntelaar actually is a perfect fit as an example for the point I'm trying to make. His overall contribution lacks compared to van Persie as does van Persie's compared to Messi.
We have to agree to disagree at that point though. Your view of the other european leagues seems to totally differ from mine. Players like Michu, Aguero, Cisse and Demba Ba walked into the premier league and scored for fun. Demba Ba significantly improved his goal scoring rates in england compared to germany, hell even Dzeko has a better minutes/goal rate in the premier league than before in germany. The premier league had the highest goals/game average of the top 4 european leagues last season. Yet you're basing your point on the opinion that it's harder to score goals in England which (sadly) really is ridiculous nowadays.
/edit:
ah, thanks, Snake

. Good to know, that I'm not fighting alone here.