Who are "they"?
The pronoun "We" includes myself, along with you and others (here, other forum members). Yet, I don't know that fiber is not an essential nutrient... I think that it is, since we don't synthesize it endogenously, we need it from plants ( essential) and it provides important nutrients (vitamins, minerals) that only come from fibrous vegetables. Fiber is not totally insoluble; that would be, er, oversimplistic.
I haven't been told how unhealthy meat and eggs are - though I have seen various nonserious news media articles that grab for our attention with such claims - I would never read them, because meat and eggs are obviously great for us.
Since Newton's First Law of Thermodynamics states that in a closed system energy and matter are conserved, I don't think that it's a lie that energy balance controls weight gain, loss, or maintenance. Further, I see that it's quite simply to measure these, so for me, stating that this is a "lie" is akin to flat earthers' silly beliefs.
The food pyramid? It's constantly in flux based on new evidence, so I don't know that its current state is meant to be compared to some prior incarnation. From where I sit, this seems like religious-type absolutist thinking instead of thinking in a manner that permits scientific processes to evolve (ha! the scientific process has led to an update - they were wrong before! so stupid!!!)
I can say confidently that I haven't been sold a single lie about diet or nutrition because I have an overdeveloped bullshit filter; matter like this post sometimes get caught in it.