When the same IP gets passed to a dozen different studios who each create vastly different experiences, that's milking and I generally don't like it. The whole point of an IP is that you know what to expect, and having different studios working on the same IP is contrary to that goal.
Nintendo does not milk IPs, IMHO. They actually put a lot of though into their games and ensuring the the experience is top-notch. Compare Nintendo Zelda games to the few non-Nintendo variants: they've all been trash. Which is exactly why Nintendo rarely outsources games.
I think a distinction is if the Publisher treats the individual development studies as functionally equivalent black boxes. With Activision's brutal management of Call of Duty as maybe the key example. Where CoD assigned studios often go bankrupt after a couple games, and several have spun off after great hardship and will presumably never work with Activision again given the choice.
One fun exception from the more "indy" side of things that comes to mind is the playfulness that resulted when Croteam and publisher Devolver let a bunch of indy developers play with the Serious Sam franchise and created some fun games in a variety of styles outside of the FPS the series is known for.
That's an overstatement: Nintendo co-develops a lot of titles with other studios, outsource a lot of their smaller IPs (mostly to Japanese studios), _and_ is being rather friendly to letting people do smaller spinoffs of their big properties.
Examples of third-party colaboration, in no particular order:
- Koei Tecmo co-developed Fire Emblem: Three Houses, did both Fire Emblem Warriors and Hyrule Warriors, which are franchise spin-offs using their Dynasty Warriors engine and gameplay, and Nintendo trust them so much that their next canon Zelda game will be a Breath of the Wild prequel developed by them, using the Hyrule Warriors label.
- Bandai Namco is more or less the main developer of Super Smash Bros since the Wii U/3DS iterations, with Sora Ltd being essentially just a consulting company run by Masahiro Sakurai. Bandai Namco is also co-developing the new Pokemon Snap, and developed Metroid: Other M.
- Capcom developed both Oracle of Ages/Oracle of Seasons and Minish Cap, two portable and very well regarded entries in the Zelda Franchise.
- On the Mario side, pretty much all of their Mario sport titles are handled by Camelot, with the exception of the Mario & Sonic Olympic series, which are published by Sega direcly, and their highly praised portable RPG series Mario & Luigi was developed by (sadly defunct) Alpha Dream.
- Then there was that time when they gave the Mario franchise to Ubisoft and they made a Rabbids-crossover, XCom-like game, which is just too goddamn funny to not put in here separately (especially since it was also fairly well received by critics).
- Good-Feel, another Japanese developer, made entries to both Kirby (Epic Yarn), WarioLand and more recently, Yoshi franchises (Wooly World/Crafted World).
- There is a metric shitton of Pokemon spinoffs (that's probably where you will find the worst offenders of bad outsourced games, to be quite honest, but even then there are series like Pokemon Mistery Dungeon, by Spike-Chunsoft, which are very well regarded).
- And as a another Zelda example, Cadence of Hyrule, made by the Crypt of the Necrodancer developers.
There are more examples, but overall a large part of their output nowadays is made by third-parties, with of course a lot of their projects - big and small - being handled by their in-house studios. That's not even counting the fact that some studios readily associated with Nintendo, like Intelligent Systems and HAL Laboratory, are actually independent (they just like working with Nintendo).
Sorry for the large response, I was bored.
Is that actually the point of an IP? I would argue that an IP is more like Star Wars where the games that can come from it can vary in format and mechanics. And less like Battlefront where the expectation is a specific set of mechanics and game modes. I would argue that if someone where to make a non RPG Mass Effect that would still be within the IP and wouldn’t go against the core concept of IP.
