Dogura wasn't emotional? And how the others Luffy, Ace and the Dadan family receive the message on his death isn't emotional, either? While Ace was shown to be bound on a tree, someone from the Dadan family says, that Luffy cried all the time and now finally fell asleep, and was still crying much after Sabo's letter arrived. Sabo's death is the reason for Luffy to get stronger, and stronger, and stronger, and stronger, and stronger, and stronger, and stronger, and stronger, and stronger, and stronger, and then even stronger to protect everyone. So that he won't have to lose anyone while it was the reason for Ace to treat Luffy as little brother and protect him no matter what.
Sabo's death had a great emotional influence on both Ace and Luffy.
Are you still dead serious on Sabo's death scenes not being emotional at all? Or have you simply not read those chapters? I know many here at MH dislike OP flashbacks because they want the plot to continue. But it's actually not that good to skip or skim through them without reading them as close as the rest of the story.
And if the death scene was "emotional" or not isn't actually relevant whether or not Sabo is dead.
What's in addition: Sabo has been much longer a friend to Ace than to Luffy. And yet, Ace asked Luffy to asy goodbye to Dadan, not Sabo. So Sabo had some years to contact either Luffy or Ace - there was always a way to do this in total secrecy. Especially if he got part of the World Revolution (Dragon showed up in Loguetown out of nowhere).