It's really just futile overall to make extrapolations for 2022 from a special election that took place under both pandemic and blizzard conditions and pre-redistricting, none of which are likely to be the case in November 2022. However, Dems underperforming 2018 but overperforming 2020 is probably not the worst case scenario for them.
Special elections are predictive of regular election results, many tried to spin the R candidate underperformed Trump, including the IA democratic party, but not on the fact that a 3 point loss became a 11 point loss which is just dowballot trends lagging. Technically Ossof also underperformed Hillary in GA-6 in 2017 but Tom Pryce had won it by 24 points (despite Trump only winning by 1) so he actually shed 20 points from his margin.
