Your first option would seem to be OK, except that I would read the beginning as the subject, whence sunt. The verb is indeed somewhat optional.
Your second one should probably have hoc nostrum commodum (neuter hoc) or haec nostra commoda (neuter plural). Hoc/haec would be the subject of the clause and should hence agree with the subject complement commodum/commoda.
A few more suggestions:
Ignorantia superbiaque adversorum nobis maxime prosunt.
"We benefit the most from the ignorance and arrogance of our adversaries." Adversorum is shorter and means the same thing. Using -que is common with parallel words. [Prosum][1]Prosum has just the right meaning:
prō-sum, fŭi, prōdesse, v. n., to be useful or of use, to do good, benefit, profit.
Ignorantia superbiaque adversorum, ecce arma nostra acerrima.
"The ignorance and arrogance of our adversaries, (behold) [these are] our sharpest/finest weapons." The metaphor of arma for "tools/means" is common enough in classical Latin (as in English).
... potestas maxima.
" ... greatest strength/power." [1]: https://
You could combine elements from different suggestions to make your own version.