Interesting question! But there is no easy answer.
Some years ago I took a B737 into CDG when CB's were forecast. The weather was not bad enough to cancel, or delay, the flight. I took about 40 minutes of holding fuel. Approaching RW27 from the north a line squall painted red parallel to, and north of, the ILS centreline for about 30 miles. Rather than penetrate any red cells I held off for (about) 30 minutes. During this time there was continuous landing traffic. The wind was very light and the cells didn't budge an inch.
I arrived at a position where there was no option but to take an approach vector to the localiser through a line squall. BANG, an immediate (but non damaging) lightning strike. We conducted an Autoland in virtually calm conditions in heavy downpour. The engineers were expecting a lightning strike and we took a 40 minute tech delay.
Now, as I recall, the Company Ops Manual gave specific advice about extra holding fuel and avoiding active cells. That covered my decision to hold off. A diversion in the Paris area might not have helped the matter; there were too many static cells to avoid. If I had returned to our UK base well, I would have been the only one! CDG had continuous landing traffic whilst I was holding. I don't recall other traffic holding off.
Moral of the story? Well, you can only do your best.