Did the Valar make a huge mistake?

[Maédhros]

Are you going to provide an argument to support this?

You bet I will:

Long they dwelt in their first home by the water under stars, and they walked the Earth in wonder; and they began to make speech and to give names to all things that they perceived. Themselves they named the Quendi, signifying those that speak with voices; for as yet they had met no other living things that spoke or sang.

The advice of Eru was in taking Melkor, which they did, lately but did.
The Valar themselves had forsaken ME, and it had many wounds which were the devise of Melkor. If the Quendi had stayed in ME they could have made ME a more beautiful place.
The back point is that the Elves would have not learned from the Valar, but they would have grown as a race, as those of the Teleri that stayed.
There would have been no Rebellion of the Noldor and the Majority of Men would have been treated better in the world.