As far as “made just to sell toys” goes, remember that, especially for it's time, the cartoon was remarkably not influenced by the toy line.
Compare it to the 80s GI Joe and Transformers, where Hasbro basically dictated development to the TV and comic writers by saying “We're phasing out some of these toys and introducing some new ones. So write out these characters and introduce these.” Hell, the Transformers 1986 movie was all about killing off all the characters who's toys were off the market and introducing the ones who'd just come out.
RGB, on the other hand…well, start with “Station Identification” where they actually took potshots at toy lines and cartoons (“Our sponsors are gonna love us for that” JMS joked in Starlog) How many of the ghosts Kenner came up with actually appeared on the cartoon? Did the ECTO-500 or the Ghost Sweeper ever make an appearance? No. (The Ecto-Bomber did, but the show had decayed so far by then that it didn't really stick out the way it would have a few years earlier)
Heck…I remember sitting at the TV in 1988 for the season premiere, half expecting the Ghostbusters to start wearing the Fright Features uniforms. It was the way every other cartoon of the time did things, right?
One more reason the Ghostbusters cartoon was a cut above all the rest. It sold a lot of toys, sure, but that was by having appealing characters and, for a sizeable amount of it's run, top notch writing and plots. The toy companies weren't writing it.