Reducing enemy Fire resistance while using Fire penetration support

Looking at a utility setup to debuff Fire resistance:

Wave of Conviction - Combustion - Curse on Hit - Flammability

so when I cast WOC, that's 91% chance to ignite for -19% fire res, and applies Flammability for -44% fire res, -63% fire res total. Edit: forgot, this also applies fire exposure for another -25% right? So -88% total fire res?

Is this inefficient when used with a main skill linked to Fire Penetration for -38%?

How much uncapped resistance does a typical lvl 83 rare have? What about map bosses? (edit: google says 30% for rares and 40% for unique mobs, is this still accruate? That seems low.) Is lowering resistance while also using a Penetration gem redundant? Should I change the Fire Pen link or my utility/ST setup?

There´s no cap on lowering monster´s resistance.
Just note that effect of Flammability is reduced on bosses.

Use whatever gives you more damage in PoB.