Regarding Dzierkals, sure he has more potential than 4th liner on Dinamo but at the same time, his skating isn't great, his shot is nothing to write home about and his playmaking ability is mediocre. Players do improve but I don't see him reaching Daugavins level. On Dinamo, sure, Redlihs and Sprukts managed to get even better numbers than that but Daugavins was a go-to guy on some very good teams and Dzierkals has long, long, long way ahead of him to ever reach that. Again, personally, I don't see it.
Regarding Bukars, the same thing happened to him at the end of last season. Really good PO on a very good team. This year, he signed with a terrible team to get the minutes and started the season as an absolute dud. So, since you don't believe in hot and cold the writing in on the wall - being an offense-first guy he didn't cut it in Extraliga, didn't cut it in KHL and was at 0,5 PPG in DEL for 1,5 years now. Which all makes sense. I'd say that's what he is going forward - 2nd line forward on a terrible DEL team, pretty solid 2nd line forward in EBEL or a star player in France and such.
So their increased production is exactly the cognitive bias you talk about. Bukarts production on a season increased by 0,02 PPG compared to last years. Dare I say, that's no real improvement. Regarding Dzierkals, sure, it makes perfect sense 21 y.o. guy adapts to pro hockey and his production is going to increase. But I don't think it's fair to put his potential into Daugavins/Indrasis/Darzins tier.