Hmm...
Let's say it this way:
When a player is awesome in a weaker league, like Netherlands, or even weaker league, like Croatia:
1. you don't know whether he is the best player there because he is the next Modric (like Modric was dominating in Croatia in a young age)
2. or he is dominating because a league is shit (like Halilovic, Pjaca for example in Croatia)
Based on performances in Croatian league alone, it was hard to tell who will turn into a gem or into a flop between Modric, Halilovic, Pjaca.
All 3 were hyped by local fans, papers and foreign fans to be the next big thing.
But once when they came into a bigger league:
1. Modric continued with his good performances and improved even more
2. Pjaca turned out to be a star of a small league and average in a bigger country
3. Halilovic turned out to be the biggest fraud of a player, who was once named the next Messi, not only by Croatian but also by foreign European papers
So, based on matches from Holland, it is a gamble to say: De Light or someone is a real deal or a fraud.
This is why we have to watch:
1. NT matches with Netherlands
2. CL matches with Ajax
3. and matches when he joins a new club
Until now, his NT matches and CL matches are a hit and miss.
In some, he is awesome, and in others, he is making tons of rookie mistakes.
Yesterday's match was not the first one.
Regarding him, let's say that I have also learned a lesson, and that nobody can claim that he will be a real deal or a fail.
All that we know is that he is good in his early age, that he is a risk, and even if he'll reach a world class level for Barca someday, it will take years of losing points and mistakes.
When a forward like Dembele makes mistakes, it isn't THAT costly, because instead of 1:0, it will stay 0:0.
If a young midfielder like Arthur makes a mistake, he will just make a wrong pass or cause a counter against us.
BUT, if a young defender like De Light makes a mistakes, that usually means: 0:1 right away.
So, I would say that it is way harder in a big team to "develop" a goalkeeper or a defender, than midfielders or forwards, since mistakes from defenders are the most costly.
In that sense, I guess that we will see tons of his mistakes like from yesterday in his first Barca's years, both because:
1. he is young
2. and it will take time to adjust to La Liga's attackers
On the other hand, in spite of his mistakes, I can already see tons of posts here: EV needs to be sacked, De Light needs to play as much as possible.
Regarding to your original point about Halilovic, let's look in a hindsight his performances from 2013/14, preBarca, when he was only 17 years old (born in June 1997, so he turned 18 after the end of 2013/14 season).
Now, imagine that we don't know how his story ended.
And imagine that a kid from this video is some new kid from Lille, Benfica or Psv who is 17 years old and is creating havoc and magic in his domestic league.
Now, honestly, didn't a kid from this video looked quite promising age 17 (awesome pace, dribbles, technique, reminds of Messi, scoring, assisting, plays as a Cm, plays as a winger, brave, motivated...).
How many people would put their money back then that 5 years later a kid from that video won't be able to play in any decent 1st division team as a starter, in Spain, Italy and Germany.
Not to many, right?
I mean, he was young. He was 17. He was young, had potential. He could have only improved after that?
Nothing of that happened:
. You have to judge every player differently and look at their skillset rather than which league they play in.
