It is if you need what the D850 can do. However, if you need a camera that is more compact, or that offers more advanced, higher quality video and live view with functional AF including eye detect etc., the D780 is better value. For some people, a Prius is a better car than a pickup truck, even if the pickup can carry more.
Haha! Value is so personal, it is a silly path to compare one's path with other's.
Cars are an example. The total market value of my wife's two vintage/ancient? vehicles is about the same as half of a new Nikon D5... but they both are priceless, comfortable, safe, reliable and economical, saving us money every day. So, yes, value is the sum of it's worth to the owner.
The D780 was designed for the market that you just described above. I hope it does extremely well!
The D850 is a fantastic camera, amazing actually. The only reason I sold it was because it added no value to my work or pleasure. Even if it did, I needed the money to pay on our medical bills. Sadly. It got us a little farther along in journey and there will be another system for sale at some point for the same reason. So, value of a product can even cross the line of what the money value will do for the quality of one's life.
A simple example is considering if a camera works for one's technical, ergonomic, spatial, and enjoyment needs. Sometimes, we shift the "needs"/priorities in our scales due to life circumstances. Sometimes we shift our desires and find the requirements which we thought were concrete have changed. Humans are like that, can't "trust" us, we are too fickle!:thumbs:
Absolutes would be so boring, I guess.