They know that devoted (absentee, early) voters are more liberal than conservative.

This is a narrative produced by the media.

85% of mail-in ballots are generally submitted by Democrats

This is a straight up lie. Colorado for example had 90%+ mail in ballots and did vote 55% Biden. Utah had 90% absentee ballots and voted for Trump.

But, they have a really good statistical model for every county

This why all bellwether counties were wrong.

You are repeating lies, and I am reasonably sure you never checked these lies yourself.