How can you say the first part? Almost all of those guys were immediate stars with the exception of Quick (goalie), Kucherov (broke out at 21) , Letang (broke out at 21, and was also the last player in this list) and Keith, who is really the only skater on this list who really spent any significant time in the minors.
I love Brown, and he bordered on it at his very best maybe hitting that level for one run in the 2012 playoffs, but no, DB is not at the caliber of player of anyone listed in my post. He was more a complimentary player like Seabrook and Sharp were in Chicago. Brown also made the NHL at 18/19, and was a star in the AHL at 19/20. And that season in the AHL was the polar opposite of this season in the AHL where the taxi squads greatly weakened the league, Brown played in the AHL that was loaded with guys who otherwise would have been in the NHL.
And how many game-changing players like the ones listed above are ever available for trade? Of the 15 players listed, none have been traded and all but one have played their entire career in one place. One is available now, and people balk at the proposed offers, even ones that don't include QB. There is no guarantee, in-fact its unlikely that in the next 5 years a player with Eichel's talent level and under-25 becomes available. The trades the Kings made that helped them win SC's were for complimentary players like Williams, Richards and Carter, not superstars. The complimentary players put them over the top because they had 3 superstars in the lineup. And no, the Kings superstars were no different than the other teams, you can't include goaltenders because as you said, the development path is different. Doughty was a borderline star in his D+1 and a full fledged star bordering on superstar in his D+2, making the Canadian olympic team and being a Norris finalist at barely 20, and Kopitar was an immediate impact player as a 19 year old in his D+2 and if you believe Andy Murray would have been the same in his D+1.
The picks of the guys taken based and my rankings of them for career...
Crosby (1)
Ovechkin (1)
Malkin (2)
Kane (1)
Kopitar (11)
Toews (3)
Hedman (2)
Keith (54)
Doughty (2)
Stamkos (1)
Backstrom (4)
Kucherov (58)
Fleury (1)
Quick (72)
Letang (62)
So yeah, picking in the top 5 matters. The Kings recent rebuild has had two of those picks, which isn't a ton for a rebuild anyways, now if one of those two is a complimentary player and we don't either trade for Eichel or try and bottom out for top 5 picks the next 2-3 years how do we accumulate the elite weapons that are needed to win SC's in the modern NHL?
The first part was simply that there are a lot of game changers who flourished early who haven't won anything, just as many are on teams that haven't won cups than on teams that have won. Nothing more than that.
Picking top 5 matters, but it's not everything. The guys above were picked between 2003-2009. There are 10 listed out of 35, and while a couple more could be added that's still 70% who didn't have that kind of an impact. But my point wasn't that picking early doesn't matter, it's that it is way to early to say the Kings don't have the game-changers necessary just because they aren't flying out of the gate like some others. Look at the Blues who won a couple years ago.
1. Ryan O'Reilly, great player, captain, leader. Broke in the league at 19 and put up two mediocre seasons. Gabe Vilardi broke in at 20, and he missed a crapload of time because of his back. He's put up substantially better numbers than Reilly did early in his career.
2. Jaden Schwartz, very good player, but not game altering - In the AHL at 21, put up 19 points in 39 games. Turcotte put up slightly better numbers despite being a year and a half younger when he started in the AHL.
3. Pietrangelo - Should probably be on the above list, he's a top 5 pick that's a game changer who came out on fire.
4. Tarasenko, in the game changer discussion - Wasn't doing well in the KHL as Turcotte, Byfield, Thomas, or Kaliyev did in the AHL. Different leagues, but the KHL is a lot more wide open, crappy defense, and at the time had the bigger ice surface, All of them are similar age or younger than Tarasenko was. Kaliyev in particular looks a lot better than Tarasenko did early.
And none of that means a whole lot because it's too early to call.
There are also high picks that started well and then fell apart, like Jordan Staal, Gagner, Bogosian, Setoguchi, and Mueller. There's a group of top 10s that scored in the 30 & 40s points wise right away then never improved on that. There's a good sized group of late starters who didn't start well but turned into fantastic players. It's way too early to tell if the Kings missed the boat on a guy like Zegras or Caufield just because Turcotte isn't in the NHL yet, just like it's too early to figure out who the true game-changers from 2019 are.
I know you are high on Zegras but 60 points next year? Sure, it could happen, but don't forget Vilardi was on a better pace as a 20 year old. I'm thinking mid 40's.