He was back for 24 games and a PO run and was going at a 50 point pace...But I don't agree with the concept that he needs to "prove he isn't a shadow of his former self". He already did that in the 2nd half.
What you just described is overwhelmingly him playing like a shadow of his former self. He was on pace for 47.8 points, so not quite a 50 point pace. Prior to last year, his lowest points pace since 2014 was 67.7. That is a massive difference. You can cite extenuating circumstances that suggest room for improvement, but that is completely different than saying he already proved not to be a shadow of his former self. Extenuating circumstances such as returning mid season, the team being bad, etc all suggest the potential for a return to form, not proof that he has returned.
The biggest cause for concern is that the 20 point drop in points pace from 67+ to 47 came
entirely from a decrease to his goal scoring output. He was on pace for 34 assists over an 82 game season, which is directly in line with his career norm (he finished between 33 and 36 assists for 5 straight seasons and was on pace before missing most of 2019/20). But his projected output dropped from being a 33+ goal scorer to being on pace for 13 goals. Tarasenko's shot is the thing that made him a top-end player and he objectively has not proven that he is still an elite shooter. He was a 12.9% shooter for his career before this season and he was a 6.2% shooter this season.
The second biggest cause for concern is that we got absolutely caved in whenever he was on the ice. He was a -7 through 24 games, which was good for 4th worst on the team. His expected +/- was -4.3 and his possession stats at 5 on 5 were atrocious. His CF% and FF% were both below 48. His xGF% was 39.99 and his HDCF% was 38.79. This was all despite zone start rates skewed squarely toward the offensive zone.
In the 2nd half of last season Tarasenko was a defensive liability who couldn't effectively shoot the puck and was on pace for 27 points at even strength. He was a good playmaker who got up to almost a 50 point pace largely by being an effective passer on the team's top PP unit. That is absolutely a shadow of his former self.
Again, the extenuating circumstances absolutely leave open the possibility that he has more to give and that it is reasonable to expect more from him this year after a normal summer, training camp, etc. But he hasn't remotely proven it yet.