You can find quite some tutorials about Rekordbox beat grid corrections on YouTube.
To bad it's all done manually per track, and not at once. Good luck with >1000 tracks...
A lot of digital DJ's suffer from this problem, and not only with Rekordbox.
It seems that the program Mixed In Key does the job better. You can use this for proper beat, key, and cue analysing, and then import the music in Rekordbox. Tutorials also can be found on YouTube.
But as always, beat grids are often as good as the music track it self. Not all are static 130BPM digital house tracks.