Asked if Bethell's runs have given him a selection headache, Stokes replied: "No, I don't see it like that.
"If it hadn't have gone well for him in those first two Test matches, that wouldn't have changed anyone's mind in our dressing room of him as a player."
Harry Brook was named player of the match in Wellington for his first-innings 123, his third century of the winter.
The Yorkshireman did not field on Sunday, when England bowled out New Zealand for 259, because of an ankle problem sustained playing football.
Brook said his ankle is "a little bit sore" and "hopefully" he will be fit for the third and final Test in Hamilton on Saturday (22:00 GMT, Friday).
England's series win is their first away from home in two years and their first in New Zealand since 2008.
Victory in Hamilton would leave them as only the third visiting team to win a three-match series 3-0 in this country.
For New Zealand, heavy defeats in each of the two Tests against England come after a historic 3-0 win in India, arguably their greatest performance in a Test series.
"We'll head to Hamilton and if we are able to get in a position of strength, hopefully we're able to put a foot on the throat and put them under a bit of pressure too," said home captain Tom Latham.
On the prospect of making changes to his team, Latham said: "We'll have to wait until we get to Hamilton, to decide what the surface is doing. Those conversations will be had once we get there."