Nor is it as strong as others make out.
In other shocking news, humans enjoy hyperbole.
The main thing about Farrell is that he is nowhere near as good as he is hyped to be; with the media particularly simply ignoring anything he does poorly; to the point blaming other players; whilst extolling the things he's okay at as being the best in the world.
He's also done most of his learning whilst occupying the England shirt - rather learning how to be a good rugby player, and THEN being picked for England - and his critics especially can't get that feeling of nepotism from his early career fully out of their minds (personally, I think that "nepotism" was more expressed by the media's unwillingness to criticise him and cut off their flow of juicy gossip and leaks from his dad).
He's an OK international player - who's a bit paint-by-numbers in attack, and who's vision and skills sometime let him down in the process - but paint-by-numbers is exactly what most coaches want from their players as it gives them control, rather than an independent thinker who might disagree with the coach.
In defence he puts in the odd dominant tackle, which absolutely does lift his team. But he also completely misses more than his fair share, and creates dog-legs in the defensive line; which only gets picked up by his critics.
As a kicker, he's OK at the international level - sorry, but 80% for his career is NOT world class he's usually hailed as being. His kicking from hand is less varied, less accurate and more conservative than his challengers - but is generally solid, and not a problem.
He is not an Iceman - he getting ever less of a Petulant Oik; but he still has that petulant streak in him - especially when talking to refs (again, he's getting better - largely by not speaking to refs at all - which is a terrible characteristic in a captain.)
He galvanises his team with his never-say-die attitude, extrovertism, and his occasional big hits.
He's also petulant with mediocre skill levels and sub-par game management.
He's a perfectly competent international FH or centre; he's not world class in anything except attitude; nor is he a liability in anything... currently (2 years ago he was for those dog-legs; and he soon will be for those shoulder barges).
The hyperbolic media circle-jerk over Farrell puts his critics into hyperbolic response (typically watered down significantly when actually put to explanations rather than 1-2 sentence sound-bites); as does the fact that his challengers for the shirt get crucified if they make the same mistake Farrell does; or ignored if they show the same good skill that Farrell gets lionised for.
And yes, I do blame the media for most of this - it enables his supporters to think that he can do no wrong, polarising the debate. Most rugby forums I see seem to be about 50:50 between his supporters and his critics (excepting the Saracens club forum, and Rugby Rebels in different directions) but the casual observers follow the media narrative because they don't know better; and media narrative has become so entrenched that they can't be more reasonable anymore as it would upset the casual viewers and lose sales/clicks (see what happened to Charlie Morgan when he went from largely-independant to working for the Telegraph).
FTR: I am NOT suggesting that his supporters on places like this do so because they follow the media line; just that the media has led to polarisation of opinion, and brought the causual observers along who don't actually watch enough rugby to look deeper than commentary.