first, those are laws for the jews to follow, yes willful sin is more serious, but they are treated the same at judgement, and souls in those verses, just for clarity means person.
This is solely for the purpose of addressing your statement that "all sin is willful". While the Old Covenant was for Israel, it still gives us understanding on many issues. So, in studying the Old Covenant, we see that there is a difference between willful sin and ignorant sin, which you said there was no difference. Now, in the New Covenant, we are still required to refrain from sin, and there still is a difference between willful sin and ignorant sin. Willfully sinning Christians are in for a rude awakening at the end of life's journey when the Lord Jesus says to depart from Him because He does not know them.
Romans 6
[11] Likewise reckon ye also yourselves to be dead indeed unto sin, but alive unto God through Jesus Christ our Lord.
[12] Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof.
[13] Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God.
[14] For sin shall not have dominion over you: for ye are not under the law, but under grace.
[15] What then? shall we sin, because we are not under the law, but under grace? God forbid.
[16] Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness?