Right off the bat I need to acknowledge that I don't watch any of his videos, but I do follow him on Strava. He is pretty interesting to follow and think about if you're interested in the limits of what purely aerobic training can do... kind of similar to the discussion of Nils van der Poel's training log and the way he "purified" his aerobic base phase.
As far as Seth goes, though... it's all base. There is no payoff. Like I said, I'm not watching his videos, but if he's claiming that he is overtrained that is nonsensical. He is significantly undertrained. Or, to be more precise, his aerobic capacity is fully developed, and his ability to train/race at anything zone 2 or higher is severely underdeveloped.
By the way, I don't think he sucks or anything. The guy has very strong PRs. His goal of an OT in the marathon is entirely reasonable. This is a guy who ran 2:23 in his debut marathon after going out under 67 minutes for the first half. Breaking 2:18 when he is able to train full-time should be imminently doable. To be honest, I'd kind of love to see him do it even though I find the whole schtick annoying.
But when I say he's undertrained, I mean I've never really seen anything like it. He's got Gasparilla this weekend and I would assume the goal if he's shooting for an OT in Rotterdam has to be around 65 minutes. Let's say 5:00 mile pace.
In 2022, he has logged four runs under 6:00/mile pace-- so in other words, he's done four workouts in the past seven weeks while training for a half marathon. He ran a 5k threshold at 5:10 pace, which is barely a training stimulus for someone at that level. 2x5k with some speed afterwards would maybe be a better approach.
He ran a 10k at 5:22 pace, which again, barely a stimulus-- that's slower than his goal MP. Maybe that's good for an easier tempo day when supplemented by other workouts. He ran 15k at 5:23 pace. Cool. That's a decent workout-- 15k at a little slower than MP. Again, you'd probably want something faster on another day that same week. Finally, he ran 20k at 5:21. Certainly encouraging, but not at all specifically tuned to the upcoming half, which is going to require a faster pace unless he's just planning to run it at MP (which, ok, that would be a choice). He "warmed down" from that 20k effort by running another 13 miles at 9:00/mile pace, which is maybe why he's feeling run down? A completely unnecessary addition to a good workout unless you're obsessed with weekly mileage to the detriment of all else.
I do wonder if he's just planning to add 5k to his threshold run every week or so until he runs 40k at MP. The way he has scheduled these thus far fits that pattern. It reminds me of the training philosophy pioneered by the great Marshall Burt. I see no flaws here: