Yes you did. For at least one season in each case. That's the point, he seems good enough and brave enough to fulfil that role. If he shows willingness to improve and doesn't get discouraged when the seniors come back, then he is perfect for your needs.
Imo, for sub players, you need to fill into one of these categories:
1. a team have let's say 4 equally as good players in one line (attack), or 2 equally good players on one position.
In that case, you don't lose any quality when you play a 4th pick player.
Examples: Ronaldinho-Etoo-Guily with Larsson and young Messi as subs.
Or Guily a starter, Messi a sub.
Or later in 2006: Messi a starter, Guily a sub.
OR: Roberto-Semedo.
2. when your 4th pick is slightly weaker than 3 starters, but he is still awesome player and you don't lose THAT much when he plays.
For example MSN+Pedro (formerly a starter) as a 4th pick.
Or something like Busi-Raki-Arthur, with Vidal as a 4th pick.
3. a player who is offering "a different option", a plan B.
As in cases of Larsson (experience, some headers and different attacking actions that 3 starters Ronaldinho-Etoo-Guily).
Or again Vidal, who is offering more legs and fighting when you need those traits in some matches or in the last 20 minutes.
4. signings for which you aren't sure how will they click.
Examples: Paco, Malcom, Gomes, Denis.
1) you buy them
2) you have NO IDEA whether they will turn into starters, squad players, not good enough (Denis) or too expensive to be subs (Coutinho)
= until you test them and find out how will they turn out, you use them as squad players for 1-2 years
5. hot prospects from La Masia. Somewhat similar example as players bought like Denis, Malcom, Dembele.
With hot La Masia products, the principle is the same, except that they came for free from La Masia.
These guys are usually 19-23 years old.
When they are aged 19-20-21, it is hard to tell:
1) whether they will turn into starters
2) whether they will turn into useful squad players
3) whether they will fail and will need to be sold
And then, while a club is giving them a probation period in a first team for 1-2-3 years, these kids are used as squad players (and they are tested and estimated all the time).
Examples: a current Alena, Puig, Wague.
But this works ONLY for hot prospects who can already offer a good sub option for a team, like Alena or Puig currently.
In the case of Wague, he seems as NOT ready in this moment to be a 2nd choice RB, unlike Alena and Puig.
So, you see, not all youngsters are as equally as good or in the same position.
Regarding Perez, for now, I see him as some kind of Montoya or Sandro Ramirez while they were here:
1. not good enough to be starters
2. not good enough to be squad players. I mean, they can play, but are you calm when a starter is injured and Montoya/Sandro need to play as starters against Real, Atletico or in a CL semis? I am not happy with that option.
My point: not every sub is the same.
And in majority of these examples from above, a sub should offer:
1. a high level of quality (quite close to a level of starters), so that a team doesn't get a huge drop in quality when they play
2. or at least: DIFFERENT options/different set of skills (and high quality)
For now, imo:
1. level of Perez is way below our sub level
2. and his set of skills isn't that different from what we have
You could argue that he is a winger and offers pace.
But that is mostly to:
1. Messi being injured
2. Dembele being injured
3. Malcom sold so that we can get money for Griezz and probably Neymar
5. Neymar, winger, not being bought in the end
With a fit team and without Neymar's sage which ruined tons of things in our team (Malcom, Coutinho, almost Dembele), Perez would never get any minutes.
Except in matches of his level: round of 64 and 32 in Copa del Rey against 2nd div teams.
Anyway, as explained above, I understand that NOT every sub needs to Messi, Larsson or Vidal.
But Perez is not the answer either.
If some of starters get injured, a 4th pick player should be good enough to play 30 matches per season. And a team not too suffer in results due to that.
On the other hand, would you guys want to see Perez as a starter in more La Liga/CL matches? I surely wouldn't.
the guy already proved he's first team material in pre-season
His preseason goals were similar to Dembele's and Paulinho's.
1. they score a goal
2. and offer 88 minutes of shit overall display otherwise
I watched all preseason matches for 90 minutes and all 3 La Liga matches.
There wasn't a single moment when I said: wow, regarding Perez, except 2 goals in that preseason matches (Kobe?) and Betis.
Alena, Puig, and even Fati are a different story.