But seriously: this may sound strange, but somehow it was a good decision to quit the band in 1969-1970. Because of that, the legendary status of The Beatles has grown to enormous heights. Should they have carried on, I'm convinced that The Beatles should not have been regarded in the way as they're looked at now.
I can see where you're coming from there.
For me, though, it's not that their legendary status grew bigger because they split up - they were already the biggest band on the planet anyway. They were fortunate enough that their break-up happened at a time so that they could quit while they were ahead.
Other bands such as The Stones saw their position in the rock hierarchy slip during the 70s because they stayed together but couldn't maintain the success they had in the 60s - there were new bands on the scene in the 70s to take over from them, such as Led Zeppelin etc.
But The Beatles split up while they were number one and they remained untouchable ever since.