Horwath
Legend
I see your point, I'll still do it my way.It's part of the Attack action but it doesn't replace nor became one of the attacks from the Attack action.
You still take actions as a Warlock.
When your turn comes and you take an Attack as a Warlock who only has 1 attack and 1 light weapon attack.
Once you attack with a club, you are done. You don't have Extra attack with club.
Once you attack with a scimitar, you can only attack with the scimitar once more and the club once as a bonus action. The club doesn't have Nick.
It's a weird case for Warlocks. They only get Extra Attack with pact weapons not all weapons.
1. It does not break anything
2. It's cool to use your pact blade and invocations if you have them
3. If you want to ignore TWF, you could take only quarterstaff and PAM
and make 3 attacks(1 with bonus action) at 5th(6th if you want to use 1st level fighter for style and mastery) for 1d10+3(+2) and possible reaction and getting +2 AC from shield.
now we can also debate does the back end of qstaff gets increased damage(no on will cry about 3 pts of damage either way), one would say that this is specifically specific situation(feat+spell combo) so it might apply or PAM damage is absolute or shillelagh damage is absolute.