My Beau, I'm sorry but your information is simply out of date.
Fenbendazole has a very wide-spread resistance problem in strongyles. You can (again) look at any number of recent studies and find this is the case. In fact, most of the benzimendazoles have resistance issues in strongyles. As far back as 2002 there are studys showing wide-spread resistance to fenbendazole by strongyles. The Horse: Dewormer Resistance in Small Strongyles
If you go on pubmed you cand find lots and lots of studies about fenbendazole resistant strongyles in horses. If you have read any of the major horse magazines in the last 2 years, you will have found multiple articles on strongyle reisstance. Evaluation of parasiticidal activity of fenbendazo...[Parasitol Res. 2008] - PubMed Result Prevalence of anthelmintic resistant cyathostomes ...[J Am Vet Med Assoc. 2004] - PubMed Result Prevalence and clinical implications of anthelmint...[J Am Vet Med Assoc. 2001] - PubMed Result Cyathostome fecal egg count trends in horses treat...[Vet Parasitol. 2001] - PubMed Result
"Dr. Ray Kaplan from the University of Georgia indicates that the equine deworming programs and drugs we used 30 years ago are now ineffective at killing small strongyles, and small strongyles are the most harmful intestinal parasite to horses at this time. To prove his point, he performed a study in 2002 on over 1200 horses at 44 stables in five southern states. Fecal egg counts were used to determine the effectiveness of each dewormer. A fecal egg count is a test performed on a small amount of feces from each horse after deworming to determine the number of eggs. This tells your veterinarian how effective the dewormer was in killing the adult worms.
Surprisingly, at over 97% of the farms' worms were resistant to Safeguard or Panacur, 53% showed resistance to Anthelcide EQ, and 40% were resistant to Strongid T. " http://www.veterinarypartner.com/Con...=0&SourceID=69
So, using fenbendazole as a main staple in deworming adult horses (where strongyles are the primary parasite of concern) is a poor choice because it is too easy to just assume that you are doing a good job of deworming when it's very likely that it's not effective.
And I would not say that the treatments you listed are the ones that the parasites "respond best to".
Migrating larva can be more easily treated and as effectively with a single dose of ivermectin or moxidectin. In fact, using power pac dosing has adverse affects that weren't recognized until 2006 so it's risk vs benefit profile changed making it a less desirable choice for treating parasites with. (It causes severe GI inflammation and even can cause ulceration after power pac dosing due to the way it kills encysted strongyles.)
Tapeworms are as effectively killed by a product containing praziquantel as by a double dose of pyrantel.
Threadworms are as easily treated with ivermectin or moxidectin without having to combine different products.
Roundworms are as effectively treated with fenbendazole or pyrantel without having to combine different products.
Bots should be treated for after the first frost and again in the early spring. Besides ivermectin, moxidectin I also effective against these.
I would highly recommend that any horse owner who hasn't already should read the 12 part series on parasites and deworming in horses that was published by The Horse magazine. It's free for download from their site. The Horse: Downloadable Parasite Series
And also view the webinar on strategic deworming that they offer (also free).
There is lots of old information out there on deworming and it can lead to wasting money on ineffective treatments and allowing for horses to become heavily parasitized due to assuming that products are still as effective as they used to be.