After all, I've expressed already my credo in this regard in more than sufficient
I partially agree, as I said
The watchdog implementations across the spectrum of '51 derivatives ranges from truly miserable to less than one in amillion chance for a missed reset when code runs away
As you see from the quote, I agree that some internal WDs are so bad that the likelyhood of them not triggering is greater than an external not triggering. My recommendation is simple: if you have to have the best WD protection you can get choose one of the uCs with a superior WD.

a BADLY WRITTEN runaway code
I have never in my life written runaway code. When you want the WD to trigger what is being executed is, not what you have written.

I hope you do not practice writing "well written runaway code" :)

Finally a note to the OP: if your watchdog ever trigger you need to fix it, the watchdog is not to be considered a recovery unit, but a fire extinguisher you want to have a fire extinguisher, but if you ever have to use it something is wring.

Erik

PS cudos to whoever it was that came up with the fire extinguisher analogy