I agree with the sentiment of this post.
However, sometimes it isn't right.
Sometimes, a champion actually is too strong, or they don't have exploitable weaknesses.
To take your example of Udyr, boots of swiftness may be to blame. In 5.22, they were buffed by a large amount, and only now are people actually building them. They cover his largest exploitable weakness - kiting. It is possible that this has actually pushed him to the point that he needs nerfs.
Sometimes when a champion is too strong they can be nerfed in a way that doesn't gut them.
Miss Fortune was given too much lane dominance by her E and thunderlord's. The nerf to her E was quite large, but she is still a competitive ADC, even out of wombo combo comps.
And finally, Lux has been complained about for a really long time - since the juggernaut patch. Few people noticed it because of first the juggernauts, then Worlds and Tahm, then the preseason, but the Lux threads were always there.
tl;dr
Sometimes nerfs are needed. It has been a while since Riot nerfed a champion into unplayability without either good reason or followup (I can remember Azir, who has such a high skillcap that he can't be left playable for normal people, Gragas, who is recieving buffs next patch, and Rengar, whose changes came with the quote "we will probably have future ones to come" and follow up buffs on the PBE).
