He was clearly just showing off to Asta and looked to get him done and that was without his magic, since Asta is a hard counter.
Lucifero could have been stronger than Lucius pre absorbing heart, emphasis on could, as Lucius' magic is touted as invincible and nothing in the world, bar Asta, can oppose it.
Which is further proven with the fact that he kept rewinding time and Lucifero had no idea about it. He absolutely slaughtered 50 percent Lucifero as well.
Lucifero and Astaroth are on the same tier of power
Even if we agree that Lucifero>=Astaroth, Lucius can at least bridge the gap. So pre eating Lucifero's heart, I have Lucifero and Lucius as going either way most likely, but I'd back up Lucius.
And this thread is of course talking about current Lucius, the one that ate Lucifero's heart, which boosted his magic. He's undoubtedly > Lucifero at this point.