most will be able to assess the old actors fairly. There was a transition from Stage to Film... and acting style took a while to adjust. Early B&W films had actors performing on film like it was 'stage'.... which comes off to most as 'overacting'. What most today do not see is that even with 'overacting' their talent was extraordinary. There is, after all, 'overacting' and 'overacting'... two very different things.
I should note: Those old actors are very much 'appreciated' by actors today.... it's the public where I am doubtful they can see the evolution.
By the 40's, (just my guess), actors had adapted to film. But the lingering effects of the stage had not entirely dissipated. But to your bigger point...
I actually agree. But not because I think actors today are 'less' talented.... rather - acting today can be controlled by tech. To be a bit gruff... if you need an actor today who must have a certain 'look' then you hire the 'look' then manipulate the performance.
Must sum this up with: I do NOT think actors today, many that is, are less talented than actors of old... I just think their 'art' is less required. - JamesJM