I actually agree very much with what you said above, it makes a lot of sense. What you said is based on facts of playing live and having some time with the amp.
Since this is the internet and everything you read even what I am about to say is to be taken for what it is, just opinion (which are usually based on facts, myth or somebody just stirring the pot). My opinion as a Herbert owner which of course makes me biased is the Herbert cuts through the mix just fine. I base this on the following:
1) I own a Herbert
2) I have listened to the Herbert with amps like Marshalls, Elmwoods, Bogners, etc... Each one has their own thing going on, but the Herbert when setup properly can cut through with no issues.
3) I use V30 speakers which are great speakers IMHO for cutting in a mix.
4) I am just cool. (Again everything you read is based on opinion)
Why do I think people say the Herbert cannot cut in the mix?
1) They never owned one and just want to be cool.
2) They have owned one and the amp they were playing up against was a more mid cutting amp and they did not take time to review the scenario. This can happen with any two amps, and cabinets, pickups, etc come into play. Maybe in a certain scenario the Herbert does not cut as well. You have to ask yourself why, if you love the tone of the Herbert and this applies to any amp what needs done to the overall mix of things that can accommodate this for your band, after all it usually applies to a band, and this is not a pissing contest between one guitar player cutting better than the other it is in a band context and you should be working together. Same thing applies if something is too mid heavy or has too much presence and killing your highs in a band, the reverse of not cutting through, you have to work through these things, review speakers, etc...
3) A lot of players are bedroom players and they are not EQ'n their amp well enough to cut with their stereos.
4) People like to hate on expensive amps and just stir the pot.
Bottom line the Herbert like most amps can cut in a mix. To make a blanket statement that it cannot is unfair and based on one scenario. If I hear things like we tried everything to make it work and could not, well I find this hard to believe. But I will give them the benefit of the doubt that with the tools they had, the ears they were using and the context of their music it just did not work. The scenario I am quoting to sounds like a fair assessment and I agree the Herbert is not a mid strong amp such as a Splawn Quick Rod, etc... They both are enjoyable to play and both give the player a totally different experience IMHO.
The above applies to most amps, not just the Herbert. I can make almost any amp be heard or get lost in a mix. I think the post I am quoting makes a lot of sense and will not disagree the mids on the Herbert is not what makes it sound Huge. The Herbert can cut in a band mix and is a fun amp to play and has a very cool tonal palate to work with. Like any amp it has its strengths and weaknesses, sometimes that is more the players fault than the amp.
Closing Note: Before every gig run an extra mic from your Herbert rig to the PA and tell the sound guy it is your other guitar players mic, unplug his mic to FOH, then put a load box between his head and speaker and push your second out of your Herbert to his speaker. He will sound and play the best he ever has and the crowd and sound guy will love how in sync the two of you are.