I like to think Gladstone proved himself the way John did--by protecting Sherlock even if he didn't know/like him that well. And I imagine that Sherlock eventually decided he wasn't a bad companion to have around. Certainly a distraction from boredom, and all sorts of use in sniffing out clues or being a diversion or giving him an excuse to chat with suspects in the park. And perhaps a bit of company when John was off with Sarah, though Sherlock won't admit it.

Thanks for commenting! I'm glad you enjoyed the story.