I think the point is that before slicing up the Audio there were no silent gaps between notes. It is only after the tempo increases that the silence appears.
@keegan.okazaki you can use this method in Cubase, but there are other approaches that are easier & produce superior results.
The Select/Arrow Tool has a mode “Sizing Applies Timestretch” where you can manually stretch the Audio Events. You could use this on your sliced Audio. But it would also work on the unsliced Audio.
But Cubase can also be set to automatically adjust Audio for the Tempo. It’s quite powerful but can initially be confusing because 2 of the main concepts have similar names but do very different things.
Finally here’s a video showing how to deal with fluctuating (and fixed) Tempos.
You should be able to slow down the Tempo, record the guitars, make sure the resulting Audio has the proper settings. Then the Audio will just follow along for any Tempo.