While Psalm 109 condemns the "wicked" for which the false prophet Paul, as "foremost sinner", is the foremost among the wicked (Mt 13:49), who as "tares", will be "gathered" and thrown into the furnace of fire, at the "end of the age" (Mt 13:30) and according to Rev 20:10, thrown into the lake of fire as well in the end.
It's not just wickedness in general, the condemnation involves not showing mercy to those he persecuted:
Because that he remembered not to shew mercy, but persecuted the poor and needy man, that he might even slay the broken in heart.
Psalms 109:16
And I punished them oft in every synagogue, and compelled [them] to blaspheme; and being exceedingly mad against them, I persecuted [them] even unto strange cities.
Acts 26:11
The unknown author of 2 Peter 3 claims that Peter is a brother of Paul. "My servant David" is not to be their shepherd until Israel has been "gathered from the nations" and returned to the land of Jacob/Israel (Ez 36:24 & Ez 37:16-25
And account [that] the longsuffering of our Lord [is] salvation; even as our beloved brother Paul also according to the wisdom given unto him hath written unto you;
As also in all [his] epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as [they do] also the other scriptures, unto their own destruction.
Ye therefore, beloved, seeing ye know [these things] before, beware lest ye also, being led away with the
error of the wicked, fall from your own stedfastness.
2 Peter 3:15-17
The error of the wicked relates to
lawlessness.
Paul's slander of Moses gives some perspective on his regard for the law:
And not as Moses, [which] put a vail over his face, that the children of Israel could not stedfastly look to the end of that which is abolished:
2 Corinthians 3:13
As for you quoting Acts, written by some unknown author, supposedly maybe Luke, supposedly maybe an associate of Paul, the false prophet, well, that is not a firm foundation. (Mt 7:27).
Do you have any reason to think that the writer of Acts was dishonest?
According to Ez 34:23, the LORD (YHWH) will judge the "flock" (Ez 34:22) but the fat I will destroy (Ez 34:16), and then I will "set up over them one shepherd, My servant David". The "fat" have already been judged by the time "David" is set up as the "one shepherd" and as the "prince" (prince being the son of the king). (Ez 34:23-24).
Thus saith the Lord YHWH; Behold, I [am] against the shepherds; and I will require my flock at their hand, and cause them to cease from feeding the flock; neither shall the shepherds feed themselves any more; for I will deliver my flock from their mouth, that they may not be meat for them.
Ezekiel 34:10
Probably this relates to the betrayal:
Three shepherds also I cut off in one month; and my soul lothed them, and their soul also abhorred me.
Then said I, I will not feed you: that that dieth, let it die; and that that is to be cut off, let it be cut off; and let the rest eat every one the flesh of another.
And I took my staff, [even] Beauty, and cut it asunder, that I might break my covenant which I had made with all the people.
And it was broken in that day: and so the poor of the flock that waited upon me knew that it [was] the word of YHWH.
And I said unto them, If ye think good, give [me] my price; and if not, forbear. So they weighed for my price thirty [pieces] of silver.
Zechariah 11:8-12