Unless you followed him closely or maybe are Dutch few expected what we saw in 2020. General consensus was he was the revelation on that Tour. So my view would reflect the majority of fans.
I'm not denying he was the (GC) revelation of the Tour, but even if you hadn't heard of him before 2021, many people on here certainly noticed him getting some pretty good results prior to the Tour, starting with the stage win in the UAE Tour, which not only lead to this thread getting created, but also to the title it eventually got (because Carlton Kirby was sure it was Harper who sprinted past Lutsenko in the final metres).
Obviously the 2nd place is the biggest result of his career so far, and I wasn't sure he was ever going to achieve something like that and not so soon either, but it definitely didn't come as much out of the blue as Froome's 2011 Vuelta, for instance.