I would endorse the approach to use fec before and after, otherwise, ignore the natural worming element / myth
Our worm management approach over the last few years has been based on FEC and SCOP advice
We have virtually eradicated (too strong a word perhaps) worms in the ewes by reacting to fec and changing the wormer as per advice
We are also fortunate to have Shona as one of our vets who came to see us a few years back to help us develop a worming plan, which seems to work
There's a lass down south who does FEC for £14. She is also a vet, Turn round is very quick