I know Disney doesn't want the expense and hassle, but why not let Mickey do it? They should be able to run buses - after all, as Road & Track famously noted, amusement parks are all about mass transit. Or maybe OCTA could be cajoled into working with ARTS to provide a decent shuttle service with limited stops and reasonable timing (not a rolling homeless shelter). I don't think the city will be able to do it on its own, politically or financially.

Disney in FL has a huge number of private hotel/resort shuttles serving the park. Most go to the central transit terminal from which park shuttles and the monorail take off. There's no ARTS there, and the shuttles come from long distances in some cases (drive 'til you can afford the room). Most also serve other parks in the area (like Universal) as part of their loop. If ARTS were bigger, rather than just a local shuttle to hotels near Disneyland, that could happen in SoCal too, leading to ... long term, a larger resort transportation district should include not only Disneyland but also Knotts (yes, not in Anaheim) and some of the other attractions in the area. Mode agnostic, though certainly starting with buses as having the lowest startup cost. Just relying on the occasional OCTA local runs doesn't do it for tourists. I do like that idea of a rail line connecting the parks (and the railroad station(s) - plural because there's one in Buena Park too though it's only Metrolink - and if possible KSNA), but where to put it and how to build it is a real challenge since there aren't any handy about-to-be-abandoned freight tracks near the parks.