Diezel's are their own thing. Peter found a niche that's not like "other" amps.
You can certainly dial them in to get "closer" to a more Marshall-type sound, yet why would you.
That said, there are plenty of Diezel flavors that give range to the "Diezel" sound. I still own 2 Diezel's, Herbert and Hagen.
Herbert is actually quite versatile, with it's 3 channels and 180 watts. Tons of gain available, yet not necessary to tap all the time. I LOVE the clean on this amp and it can literally give you a lot of different options tonally. Adjustable mid cut, channel 2 has two modes, individual channel volumes and well as dual Master Volumes...The channel modes on channel 2 make it very cool, blues to crunch in the flick of a switch. Channel 3 is every METAL guy's dream, yet can also be used as a great lead option to a crunchy channel 2 if the gain on ch3 is dialed back a bit and a little volume boost is added. Again, lot's of options. Tight sounds.
Hagen is totally different, yet again Diezel. More open is what I've heard many say. It's got 4 channels, like the VH4, yet with a different character that I think is more usable across the spectrum. Nice clean, yet push it a bit and it's AC/DC-like crunch. Channel 2 picks up where ch1 stops and can get more crunchy, basically you have 70's tones on up with 1 and 2. Channel 3 starts to ROCK harder, yet still with that "open" quality. Channel 4 is more than I need most of the time, yet can be a great lead option since each channel has its own Master Volume, Gain controls, and EQ section. Shift the EQ and add a bit of volume and searing leads abound from here.
I let go of my Einstein and my VH4. Haven't tried the newer VH2, Big Max, etc...They are kind of of shoots of the originals, IMO.
I feel like I'm covered with these two amps. Not that I don't own plenty of other kinds of heads.
So, if you are trying to compare Diezel to other amps, don't bother...they are their own animal. Like a Mesa Mark, it's not like other amps.
If you are simply asking where the gain structure lives, that really depends on the user. Diezel can do some amazing cleans, great bluesy tones and gets excellent lower gain sounds as well, although they are clearly more well known for the more BRUTAL tones.
Well known users, Metallica, Tool AND many studios.
In fact, Tim Pierce, amazing player and go-to studio guy has a VH4 that you've probably heard on many albums and would NEVER think it's a Diezel. He's not necessarily known for being a HIGH GAIN guy, more of a super tasty player with amazing phrasing.
Long post, hope it helps.