Alternate picking doesn't sound right in playback

This is so normal.

e.g.: I play the piano, the playback on the computer of the score I wrote in any note writing software has nothing to do with the piano I play myself. Because the computer doesn't knows neither keystrokes and velocities, nor my timing.

The guitar is more nuanced than the piano in terms of playing style. The sound changes depending on where you play the string (near the threshold, sound hole or neck), whether you play it with a pick, finger or fingernail, and your picking strength and direction (up or down).

Because while you play the guitar, you use many hand and finger skills that you have acquired, whereas the computer plays the notes in a robotic and mechanical way.

Maybe in the future it will be possible to virtualize it (by adding many hidden nuances/playback parameters in addition to velocity).

In what way does it not sound right? Can you post a link to a video of what you are expecting? What do you mean by, "no correct values for the notes"?

Have you loaded a soundfont which sounds like your required guitar playback and has the different variations of picking styles that you need, and then applied this font to the individual notes, taking care to apply volume changes too?

As has been said already, these things are probably best left to the human performer unless you are willing to spend a lot of time 'humanzing' your score playback. I spent hours doing this to one particular score and it's debateable as to whether it was worth the effort.

ZMD (above) is so right about all the nuances that could apply.

You wrote:
...it does sound better but still not what I play with the guitar.

For that to happen you should use a microphone and some recording software to produce an audio file of your actual performance. This way, when played back, it will also sound exactly like the make and model of the guitar you use.
;-)