Don't forget his special armour and sword too. I'm expecting 3-4 more things like that plus a revelation that the Demon Lord totally threw the towel and could have easily dominated him during their last battle.
I think the series nail how Dan is a washout from an old era and everyone acts accordingly. But at the time to showcase how strong him in his prime was it tends to fumble quite a bit.
Plus the rate he regains/loses strength is weird, like he has the whole training to get back a bit of his power that lasts for like 5 minutes and then go back to the start.