You wanna tell me your source(s) for that?
Aside from that, I kinda agree with @Weiss in that it’s basically a living feeding trough, which imo isn’t a very useful niche. I suggest that it serves as a egg-incubator, it can be commanded to sit on top of an egg and keep it at the right temperature. That could be a little OP though, maybe it should be harder to tame than you suggested. There could also be some exeptions to what it can incubate: not wyvern or drake eggs (due to the temp requirements being to much for the maiasaur), it also can’t incubate eggs too large too sit on (gigant eggs, bronto eggs, etc).
Additionally, it could serve as a feeding trough, but towards pregnant animals as opposed to babies, the maiasaur will keep the gestating female at full food, while sacrificing its own hunger (but at a lower pace than the pregnant creature, otherwise it wouldn’t be worth taming).
Just some more ideas, not saying yours are bad, simply stating my own.