I like Gilmour but I really can't see a team moving a top 4 defenseman him. Recent history suggests that he'll get something like a third round pick and a later pick. Webb will get less than that if a team is willing to use a spot on him.
Every team has the capacity to make some big trades so we'll see what happens. I was only making an assessment of the current situation.
I will say, however, that adding a pair of top flight defensemen without an OA spot is no easy task and it's not a given that they will be able to do it.
I think your underestimating the value of a D who was good enough to have a solid playoffs against top teams. Webb 6'4 200 and is not flashy but gets the job done. Physical presence and leadership qualities are an asset. Davis went for a 3rd, 4th, 5th and rights of Marshall Warren and Webb is a better D. I would keep him and if Coskey or Prosvetov make the next step then he will be a great help being the only RD on the team.