Devout Christians sin. Every day. And there is no magnitude or gradient for sin. In God’s eyes all sins are equal.
No one is totally perfect except Jesus. So, yes, Christians sin also. But the inward working of the Holy Spirit changes us day by day, so that we don’t have the same sinful lives as we did before we were saved.
And as for all sin being equal, that doesn’t seem correct. When Jesus spoke to the scribes and Pharisees about their sin, he said they would receive greater damnation. So, obviously, some sins are greater than other sins.
“Woe unto you, scribes and Pharisees, hypocrites! for ye devour widows’ houses, and for a pretence make long prayer: therefore ye shall receive the greater damnation.”
(Matthew 23:14)