I don't see any reason not to take Burgess at his word.
After the World Cup, the current season will bring a Six Nations championship and another season where Bath (beaten finalists last year) will try and win the English Premiership. Bath are also in one of the toughest Champions Cup groups, where they face Toulon, Leinster and Wasps, who all won the top European title under the old Heineken Cup name. The season ends with a three Test tour of Australia. That's quite a schedule for the next nine months or so. The main concern for Sam Burgess will be pacing himself, given that he had no real break after League, and hasn't had a proper pre-season yet.
The following year, the 2016-7 season ends with a Lions tour to New Zealand. If Burgess is making a consistent impact at international level, then he'll have ambitions to be selected for that. At the end of the Lions tour, we'll be two years out from the next World Cup.
If Burgess is succeeding, then there are a lot of big occasions to keep him occupied, and that's the main reason he made his switch.
There's no guarantee he will succeed, however. England might have a poor World Cup, and it will be no fun being part of that. Also, there's still a lot of doubt about his position, since Bath will play him as a flanker but England aren't convinced he can do that job yet at Test level. You can't be a forward for your club but a back for your country for any length of time, so he'll have to make his international case all over again.
Whatever strategy you choose on the pitch, you have to be able to execute. There's no guarantee the New Zealand could produce a side to do that.
This idea that the All Blacks had never heard of the drop goal until recently is ridiculous. Even in that infamous 2007 quarter final, Dan Carter was trying to edge his side further ahead through drop goals as early as the 52nd minute. The All Blacks were leading 13-6, and Carter went for the posts from the 10 metre mark, pushing it well wide.
When New Zealand said afterwards that they didn't practice drop goals, it's obvious they didn't mean they never intended to use them. The only conclusion to draw is that they didn't practice, because they were confident they could perform that skill whenever it was required. After all, Zinzan Brooke never practiced but claimed he was able to slot his 1995 World Cup drop goal with ease, because of all the rugby golf he played in his garden as a kid.
However, it's not an easy skill to perform when the weight of a nations's expectations are on you, and the clock is ticking down to send you home. As it turned out, New Zealand did need the practice.
New Zealand have always played referees well, and I say that admiringly, not begrudgingly. There have been no laws or interpretations to stump the All Blacks brains trust over the years.