Ramsdale is average statistically and doesn't pass the eye test. I've watched 90 percent of Bournemouth's league games this season and he's far from the finished product. He has a lot to do which perhaps clouds people's judgement. It's often the case with keepers from relegated sides. Potential sure but not more than 10 millions worth imo.
Was just looking at this and average is pretty much spot on - if not actually a little generous. Taken from
FBRef.com:
Save percentage (shots on target that he saved) Ramsdale ranks 15th with 68% saved. For comparison Henderson was 3rd with 75%.
Post-shot expected goals, minus goals allowed (essentially how many goals "should" he have conceded from the shots faced, minus the actual number of goals conceded) - ranks 17th. Faced 62.1xG of chances, conceded 62 goals. Henderson ranked 6th - faced 37.6xG of chances, conceded 33 goals.
% crossed stopped (crosses into the penalty area that the keeper caught/cleared) - Ramsdale ranks 14th with 6.2%. Henderson 5th with 7.9%.
Defensive actions outside penalty area (how much "sweeping up" they did) - Ramsdale 14th, Henderson 12th.
Completion % on passes over 40 yards - Ramsdale 18th, Henderson 20th.
Statistically he doesn't have a standout attribute. And like you I've watched him loads this season and haven't seen much that makes me think he's more than an average Premier League goalkeeper YET. And that's the big thing - we're never going to get Henderson permanently, so if this is our chance to sign our GK for the next 5+ years, and have him develop into something close to what Henderson is NOW, then I think it does make sense to take it if the price is right.
Pretty confident that whoever we have in goal next season will not be as good as Dean Henderson regardless.
Edit, oh I see you've found a quote from someone else saying more or less the same thing

never mind, I learned something today