Selling Savinho is a risk either way.
If his goalscoring at Girona was an anomaly, £67m is a decent fee, and Rodrygo is probably a considerable upgrade
If his goalscoring at City was an anomaly, we would be making a mistake selling him, even/especially at £67m
Some stats/maths to back this up:
At Girona, he outperformed his xG, scoring 0.27 from 0.18 (150% of what he 'should' have got)
At City, he underperformed his xG, scoring 0.05 from 0.25 (20% of what he 'should' have got)
His performance in terms of expected assists is good and improving (0.24 xA and 0.35xA) I prefer to use xA rather than assists because it removes the quality of ST but his Assists per 90 were 0.30 & 0.41 respectively.
If you combine his Expected Assists per 90 from City and his Goal overperformance from Girona and calculate that over an entire PL season of 3420 minutes you are looking at a wide player who finishes the season on 14 goals and 13 assists. In all likelihood he would finish on more assists (16 based on actual assists) £67m is a bargain for such a player, nvm someone 21 years old.
If you just take his xG for City last season and have him meet it, you're talking 10 goals.
I'd be much more comfortable selling him a year from now when we get a better idea of his goalscoring ability. I personally find it difficult to believe that 0.05 from 0.25 is not an outlier, it's a crazy stat.
Obviously the coaches, analysis teams etc. see him in training every day, so will have a better idea than any of us. This is the kind of thing they're paid to get right.