Black/brown bears are larger than tigers, but tigers have longer teeth, sharper claws and are faster, more muscular, agile, intelligent, and aggressive than bears. Think of whipcord Bruce Lee fighting a flabby bar brawler who is ten inches taller and 100 pounds heavier. Siberian tigers (slightly larger than a Bengal tiger like Shere Kahn) actually prey on bears.
Baloo is drawn as a standard black/brown bear. While India does have black and brown bears, they live up in the foothills of the Himalayas. A bear encountered in the middle of an Indian jungle would most likely be a sloth bear, which is a smaller species.
Yes, but bears are hardly flabby. They've been known to crush the skulls of bulls and tigers with one swat of their paws. Baloo was no weakling. In his 'Bear necessities' song he uprooted an entire tree to use as a back scratcher.
Simply put Baloo was stronger than Shere Kahn but Kahn was so hate crazed that he overwhelmed Baloo.
Tigers are actually bigger than lions, just an FYI. What I think it came down to is that Baloo was basically a peaceful fun-loving pacifist while Shere Kahn was a ruthless killer.