The Cubs have told Mike Montgomery, and anyone asking about Montgomery, that he is a bona fide major-league starter. “I really think this guy’s capable of 10 to 15 wins if he’s given the opportunity,” manager Joe Maddon said — last spring. But, if anything, the left-hander’s chances of ever becoming a bona fide member of a five-man rotation for this team have gone from slim to slimmer since then and are fast approaching none with the signing of Yu Darvish to a six-year, $126 million contract. That deal put five multimillion-dollar starters under club control for the next two years — three if Darvish doesn’t exercise his opt-out clause after 2019. And that doesn’t count rehabbing Drew Smyly, who could enter the mix next spring after signing in December. So what happened to that “capable of 10 to 15 wins” sentiment the staff and front office keep talking about? “I hear you on that,” Montgomery said. “I think I’m going to be a really good [starter].” He has shown as much in 19 starts for the Cubs since being acquired from the Mariners two summers ago, including 14 as an injury replacement last year that might have been the difference in making the playoffs. Montgomery, 28, made those feelings clear in December when he spoke up about wanting a legitimate shot to win a starting job and to avoid the swingman role that he considers a potential health risk.