Don't think we have scouts in Netherlands. Missed out so many good players from Ajax in recent years.
Well, we signed Cillessen.
Don't really agree with your point though.
Look at this list of the players they've sold and tell me who you think we should've signed.
https://www.transfermarkt.com/ajax-amsterdam/alletransfers/verein/610
I think Eriksen and Davinson Sanchez are the only one who would have a place in Barça. But we didn't really miss out on Davinson since he rejected us to sign with Ajax in 2016 and this summer we were never after him (and even if we were he would probably reject us again because we still couldn't guarantee him playing time). We clearly knew him before he even signed for Ajax though and also followed him there.
I've also liked Bazoer and don't know how he's doing now for Wolfsburg but didn't hear any rumours linking him to a top level club so I don't think we should really be sorry that we didn't sign him.
So I think Ajax didn't really sell that many good/great players over the last 5 years that we've missed out. But it's clear they do have some talented players right now and we are surely following De Ligt and we were also linked to Dolberg and Donny van de Beek. So I don't think our scouting in Eredivisie or around the world is really that bad it's just whether our SD decide to go seriously after those players he has a good scouting reports on and if those players even want to come here or if they prefer other clubs for different reasons.