The show often suffers from the mentalist using the power of script, but all character-based shows have this tendency.
No, just the badly-written ones.
Beg to disagree. I was fan enough of Wire in the Blood to Netflix all the episodes (so far as I know) and watch them all, even the Texas one (
.) But even Tony Hill used the power of script. It is part of the nature of the beast. Character-driven shows depend on the viewer investing in the specialness of one or more characters. It is intrinsically hard to write a series of scripts in which this specialness is manifest, episode after episode, in a genuinely organic and plausible way. One of the most consistent was the Sherlock Holmes stories and there were plenty of those in which the "deductions" were not plausible.
Malcolm McDowell's cult leader did not need to be written into the moronic Red John storyline. The completely unreformed nature of the character would have been a severe challenge to Jane, who was once the same kind, and still isn't as different as he might like to flatter himself.