There is very few "top clubs" tbh and I am interested to know your criteria for such definition.
Valencia can be considered a top club for example,they were coached by former GK and he has transformed them into a very young talented team that reached the CL.
Zoff coached Lazio when they were still a top club too.
If you aren't considering those top clubs (which is justified) then you also face the fact that there is very few sample size of big clubs and GK is one position in football out of 11 and there is those who didn't play football so the chances of a GK being a coach is like 1/11 or 1/12.
Again,very small probability with very small sample size even for "just saying"
Goalkeepers vs field players 1:10 (out of 11 players).
In theory, that means that 1 out of 11 coaches could be a GK.
Since 2000, Real had 14 coaches.
Barca had 10 coaches.
Bayern had xx coaches.
Juventus had xx coaches.
xx coaches won La liga since 2000'.
xx coaches won a CL since 2000'.
xx coaches won La liga, EPL, Bundesliga, Seria A, French league 1 since 2000'.
That is a sample of probably 50-100 coaches when you put it that way:
1. coaches who coached top team (Barca, Real, Bayern, Juve, Man Utd, Chelsea)
2. coaches who won league championships in top5 countries
3. coaches who won a CL since 2000'
I didn't checked all of then, but from my memory, I don't remember any goalkeepers here under points 1, 2 or 3 (from above).
So, yes, I know that majority of coaches will be former field players since there is 10:1 ratio in field players vs Gks.
But even then, out of 100 coaches (in my criteria from above), you would expect around 8-9-10 former Gks (out of 100 coaches in total) on that list, if this would have been just "a number's game" and if we don't see former Gks coach big teams ONLY because there is 10 times more field players.
In short:
1. yes, there is 10x times more field players versus former goalkeepers among coaches
2. but still, field players, especially midfielders and attackers have an advantage in being future coaches since they have actually lived and played as midfielders/attackers for 20 years and they know majority of tactical tricks in the book from first hand, unlike goalkeepers.
So, when an opponent presses you, a defensive midfielder/midfielder will know from first hand 10-20 ways how to neutralize that pressure.
A Gk will surely know some tricks, since he listened a coach in a locker-room plus he was on a field in those days, but still...
Imagine 20 years from now.
Would you rather give a chance and have more faith that he will lift our team to glory:
1. a future coach Mats
2. a future coach Pique/Masch/Umtiti
3. a future coach Xavi/Busquets
So, yes, I personally have more faith in midfielders compared even with defenders, even though there was a lot of good coaches who were former defenders.
I am not implying that the best dribbler (for example Ronaldinho) will be the best coach.
But, imo, with Guardiola as a player, you could have seen that a guy is Einstein even as a player and that he had insane (tactical) computer in his brain.
He wasn't THAT much technically gifted, but his understanding of a game and tactics was always superb.
Lucho, on the other hand, as a player, was always a fighter and a crazy runner, who relied more on emotions/heart/stamina than on IQ and understanding of tactics.
He played more with his heart than with his head. Imo, he is quite similar as a coach also (the same as how Pep is also similar to himself as a player).
Rijkaard was a defensive midfielder at AC Milan in late 80s and 90s, when Seria A was the best league in the world and where tactics were the most important part of a game.
So, if he played as a brain (defensive midfielder) in that league for a few years, he surely had more "first hand" experience about tactics, defending, how to press and how to neutralize opponent's pressure, how to positionally perfectly defend against counters, how to outplay opponent and how to get outplayed by opponent, than his teammate who was a GK in those years.
So, imo, there is some relation between:
1. player's position during a footballing career
2. player's/coach's general IQ as a person and as a player
Just one analogy: we all know Alexis Sanchez and how he played while he was here and about his low IQ.
Now, imagine him as a coach in 10-20 years.
Would you rather have midfielder Xavi or a Gk Mats, plus again, an Einstein on a field (Xavi) or Alexis, who was never a too bright guy.
I would pick Xavi in both cases, that is a no brainer.
Of course, everything written above is not set in stone and there are lots of examples of a guy being a brave lion as a player, and now playing as a chicken as a coach.
Or a guy playing attractive football as a player and now playing like Koeman as a coach (and vice versa).
But in general, imo and stats would probably backed me up if I digged deeper: if you go with a midfielder/attacker + a smart former player + who has some coaching experience and some nice results behind him = your chances of getting a good coach will grow a lot.
Add here: Barca's DNA and similar...
For the end, I would always go with a former defensive midfielder/midfielder as my favorite position (for a future coach) in terms of tactics, especially compared with former goalkeepers.
Here is one of our former coaches, also a former defensive midfielder (the same as Pep):