Where did Pronman say he "never bothered to scout" Seider? I'm genuinely unfamiliar with that piece of info. According to this article (by Pronman) it sure seems like he scouted him.
"Moritz Seider, RHD, Detroit
Seider was a unique evaluation in 2019. He played in the Deutsche Eishockey Liga (DEL), not a league many were used to contextualizing top-10 picks in at the time. His club in Mannheim was very strong, and he didn’t receive a ton of ice time or power-play opportunity. You still saw this huge, mobile, competitive defenseman with some puck game and it was clear he was a very good prospect. Whether he had the offensive upside to be a true top-end prospect was the question for myself and a lot of NHL scouts. I rated him as a mid-first-rounder.
There probably wasn’t the evidence at the time to support what he’s done offensively since then, but there was evidence to suggest he was going to be an excellent two-way defenseman. Seider went to the U20 B pool that winter and was the clear best defenseman, helping elevate Germany to the A pool. Even that, while impressive, is not usually indicative of an elite prospect.
His world championship was different. He showed up for Germany versus some of the best players in the world and didn’t look like a fish out of water. It was around that time I started to hear from NHL scouts that this player was for real, and it was here that I erred in not valuing how good he looked for a U18 defenseman at arguably the second-highest level behind the NHL. I don’t think I would with that information have moved him up to a top-five range as he’d go now in a redraft, but he should have been rated as a very reasonable top-10 pick."
https://theathletic.com/2952636/2021/11/16/pronman-nhl-prospects-i-was-wrong-about-the-2021-22-edition/