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So I play on a Bruckner (still love it) with a Mike Finn 3H and have found my sound to be too diffuse for that kind of full yet percussive like sound I’ve been listening to with blasmusik.

So I’ve been experimenting with a Laskey 30C just for fun thinking that a shallow cup mouthpiece would be stupid and that those mouthpieces are inferior to the helleberg.

Not only is my sound less diffuse, and more direct I have also found that I can get more color with less effort. The horn still plays in tune… maybe more in tune.

TLDR

Maybe some of those German tuba players are onto something by not playing on the biggest funnel shape mouthpiece they can find.

With a pure/(potentially, when playing) pretty-sounding lip vibration, shallower mouthpiece cup depths and shapes become options (rather than relying on "bucket" mouthpieces to cloak impure lip vibration.

In the past, there was far more emphasis on making a nice-sounding lip-vibration (aka emphasis on "tone") than there is, these days.
Today, everyone seems to talk about "air" being the answer to everything, and no, air is not the answer to everything.

Re "use of air" theme, I agree that a ton of air does not solve all problems. However, I feel that air FLOW is very important; i.e., keep the air flow constant to whatever extent is necessary to support the phrase and melodic line. Sometimes that can mean a slow, warm air flow. Sometimes it can be a relatively short hurricane volume of air, so long as is necessary to preserve the composer's musical and dynamic sense. (I realize there is nothing new or profound in what I have written above.)
ACE

"Mashing the proper buttons" and "blowing through a correct length of pipe" are remarkably helpful as well...

...but quite a few seem to discount the second of the two I just listed.

bloke "ie. It is I - TubaHero - who plays in tune. I NEED NOT play a tuba that is easy to play in tune."