Getting along doesn’t mean we’re the same, Buddhists get along with many Christians too.
And they aren’t the same on the level of ultimate reality, they don’t agree on what Nirvana is, which for many Mahayanists is a form of eternal spacious consciousness (albeit an empty one). Even Mahayanists don’t agree on the nature of ultimate reality, see for example the debates between the Gelugs and the other Tibetan schools. No Theravadins I know of accept that the Buddha is eternal or that various Buddhas will take you to a pure land if you pray to them. That’s pretty “ultimate reality” and yet they disagree there too.
The very idea of neyartha and nitartha as being ontological - “relative reality” and “ultimate reality” is actually a later development too, in the suttas these refer to hermeneutics AFAIK.