I say this again, it's a moot point to compare Sainz's testing race sim with Max's race stint. Max was having a lazy drive last year after putting distance to the next car. The track in testing is way more rubbered than for a race. Any race sim done today (3rd day), if compared to last year's race stint, is going to be even bigger of a sham.
The ideal comparison is to Ferrari's own performance from last year's testing. To that extent, the progress appears to be quite big! If we get to see Red Bull, Ferrari, McLaren, Mercedes and Aston doing a race sim today, it would give a decent comparison of their relative standing. Even then, some teams might do a few things to mask the real performance.