Yes. Less so for Seider as he was coming out of the DEL and younger than the other two.
Flip side... Were Hedman, Ekblad, Dahlin, Werenski, Hughes, Heiskanen, Drysdale irreparably harmed by playing as teenagers?
Well if I may use the trophy argument;
Makar (24) - Calder, Norris, Conn Smythe
Fox (24) - Norris
Seider (21) - Calder
All three are defensive zone beasts. Hence why the former two are Norris winners before age 24.
The rest;
Hedman (31) - Norris, Conn Smythe (took him until age 27 for first trophy)
Ekblad (26) - Calder (at 19, struggled for a few years and then caught up)
Dahlin, Heiskanen, Werenski, Hughes are all #1D (Drysdale isn't quite there yet) and Dahlin/Heiskanen are a cut above the other 3 currently, but they're 1st and 3rd OA picks. Edvinsson was 6th and not as NHL ready as either of those players.
Luke Hughes, Jake Sanderson, etc taking 2 years post draft. #1 OA Power taking an extra year in college after having spent his draft year there is already reaping rewards for the Sabres thus far.
So the argument goes both ways, but generally to complete and maximize a D's 200 foot skillset, you'd be best letting him dominate a league before heading to the NHL. You can learn that in the AHL, they're not just total scrub coaches and players down there. Lots of cup winning NHL coaches and coaching staff come up from that league.