If the raker is adjusted to the corresponding cutter then the chain will run true, It's not just about making the chain cut faster, it will also be smoother. Maybe you should try it, rather than arguing about it when you have no experience on a topic. You actually sound like a smart individual, but sometimes that can be a downfall. I've been humbled many times trying something I didn't think was going to work that was told to me by someone with less experience than me on the topic, sometimes people with no/little experience are not caught up in the "how things are supposed to work or be" of it all. That being said, other times someone else has tried our way and knows what works best so they offer up a little tip and we have the opportunity to learn.
Let it be know, I think the perferd/stihl 2 in 1 is a great tool, but as you've said after a bit the chain still needs to be trued up. Why is that, if it's working so well? Rather than taking it in next time, spend your money on a progressive raker guide and give it a try. They are not too much at the dealer, that is if you're not afraid to walk into a husky dealer

. Stihl has some too, but they are a bit different and are not available in our market(I had mine shipped from Europe), and they are quite a bit more aggressive even using the hardwood setting.
Here's the one I like for 3/8 chain. You get the same settings as the one on the roller guide, but since you have the 2-1 it will hold your file up on the cutter nicely and there is really no need for the roller guide in that case.
https://sherrilltree.com/husqvarna-depth-gauge-file-guide-3-8in/
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