The Baggies signed off their 2016/17 season in defeat to finish off a miserable final few months.
Albion all but secured their Premier League survival in February but then failed to win another game since the final fixture in March after another defeat at Swansea.
Backed by more than 2,000 travelling fans, Albion took the league in the 33rd minute when Jonny Evans capped an impressive campaign with a trademark header.
Pulis' side looked to be heading for victory until poor defending let Jordan Ayew equalise in the 72nd minute before Fernano Llorente's late winner.
"I'm desperately disappointed the lads have got nothing out of the game today, because they deserved it," said Pulis.
"Their first goal is shocking defending from us. For the first hour, I thought we controlled the game. The lads have worked really hard this year. We've got punished in both [final] thirds of the pitch at the end of this season.
"I'm more concerned about making clubs better, wherever you finish. We've done better than what we did the previous year."
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