Whether Barca was their home or not is secondary. The aforementioned players were young, and didn't hit the ground running. But the coach persisted with them. As for Neymar, he was a big marketable talent, but there was a lot of skepticism when he moved to Europe. I'm sure if you checked the Neymar thread, you will find many ppl showing reservations, most notably the leader of the pack, the honorable BBZ. Neymar took time to adapt and had to overcome his own struggles. I wouldn't say he was already GREAT as he's become today.
The difference between Neymar and MAtS' situation is not one of proven quality at the time of acquisition, but mostly about position they play. They were both talented youngsters. Only Neymar's poor spell of form, even extended ones, can be bore without having a negative impact overall but poor form or error from the keeper mostly proves fatal to the team.
Don't agree. First, Busquets had a very fast impact in the team. First season in and he was performing amazing, including in the clasico when he obtained the penalty Eto'o missed. Both Busi and Pedro had great first seasons. Busquets has a very good 2008-2009 season, that's why he played in front of Yaya Toure. Not because he was playing so-so, but the manager trusted him. I didn't see Busi playing like shit and still being trusted over Toure because he was young and promising. He earned his place. Something Stegen never did over Bravo, keep in mind.
About Neymar, some were skeptic. Not me. Neymar when he came at Barca was 2 times the player Stegen is now. That's why teams wanted him and were willing to pay crazy money to land him. Maybe the talent is the same in both, but Neymar as a player was more evolved than Stegen is now.
I don't see why different rules should apply to Ter Stegen. You're not good enough, you don't play. I'm not a fan of the idea that a player should be trusted in important games in order to develop him, and least of all a goalkeeper. Other teams develop players, we usually buy them, unless we are talking about Masia players. PSG developed Ronaldinho, Mallorca developed Eto'o, Sevilla developed Alves, Monaco developed Giuly, Lyon developed Abidal and the list goes on and on. We are not the kind of team to use players that are not ready in important games in order to develop them. Arsenal is that kind of team. Not us. Our policy in recent times has been buying top players to fill the spots for which La Masia could not provide us with class options. We thought that Stegen is that top player, but as it turned out, it's actually Claudio Bravo.
Some even said at the begining of the season that Stegen should play La Liga instead of Bravo, a few weeks after Bravo captained Chile to a record Copa America campaign.
What was that? It's like saying Rafinha needs to start instead of Iniesta, because he is the future. We are Barca, we live in the present. Whoever is the best should play. I don't care if that person is a 35 years old Iniesta or a 35 years old Bravo.
When Ter Stegen plays and concedes like crazy,it's excusable because he has a terrible defense in front of him.When Bravo plays with the same defense we rarely if ever concede,so i guess we all have been blind and Bravo actually plays with Puyol,etc...which explains the discrepancy between our defensive performances. 
. Note to self: do not read barcaforum late at night 