Just bought D4 , linking accounts question

As i have more games of Blizzard on Battle.net i bought game here, so i just linked my battle.net account to steam, what this linking gives, only progression ? can i see Diablo 4 playtime on steam ? i don’t understand whole linking stuff

Linking is required because a battle.net account is required to play all blizzard games. Blizzard saves all your progress in your games on their own servers, and for cross-progression to work, all platforms must be linked to battle.net servers.
Linking your battle.net account to steam does not give you access to Diablo 4 on steam. Battle.net and Steam are two seperate clients, You wont get statistics and achevments on steam, when playing the game on the battle.net client.

refund the game as long as u can lostboi

No, i’m not so sensitive about all drama around Diablo 4 , campaign is enough for me and maybe mp later

I have D4 on my computer though Battle net. I just bought D4 for my son on Steam. when he loaded it we found that all he loaded was a duplicate of my battle net account. and of course we cannot play at the same time.
Help!

This happens if the battle.net account and steam account are connected. I would assume that you own both accounts, and your son is using your steam account?
In order for your son to have his own game save he needs his own account, there is no way arround it. Cross progression is not optional.