I'd argue the Harry Potter books were more popular than the Marvel characters ever were (at least with kids), which gave the Harry Potter film series a huge boost of interest and associated box office success.
I'm not sure how them being dedicated to their own franchise diminishes its popularity any.
It is true on average each film makes less than the Harry Potter franchise, and in that respect it's less impressive, but it's very impressive seeing what Marvel Studios has accomplished in the 7 years since Iron Man first released.
Numerous films, plans for numerous more, more than half a dozen spin off TV shows, etc. It really is incredible what they've accomplished, both in terms of financial success and internal narrative spread across a number of films and TV shows.