I don't think it's only about looking at the history of #10 draft picks. Because the decision to trade Saros isn't going to come down to who we think we might get out of that pick (4 or 5 years from now or whatever it will take for them to develop). It's going to come down to evaluating Saros' performance, his contract expectations, and how competitive we need our team to be in the shorter term.
If the organization feels it needs to maximize its odds of maintaining a minimal level of competitiveness, and if Saros' contractual demands aren't crazy, then we'll keep him, we won't care that 1 in 10 past #10 picks turns out to be a star player. If we determine instead that we can take the risk of not being competitive (or even actively want to tank), or if Saros' contract demands are too extravagant, then we'll trade him... and then it's not going to be about the value of the #10 pick in isolation, it's going to be the value of that pick in relation to any other offers we might have on the table for Saros because we'll just take the best offer regardless.