There are multiple ways to decompress BRs beyond just increasing the upper cap.
Frankly, I think the most-unexplored route is adding more digits to the BR range.
We currently use X.3, X.7, and X.0, why not also add X.1, X.2, X.4, X.5, X.6, X.8, and X.9? Then there would be far more slots for a machine to go to where it doesn’t get stuck in the awkward situation of “move it down and it clubs, move it up and its worthless.”
Under such a system, I would start placing the Jumbo 75 at 5.4 BR, and the Jumbo 76 at 5.8-6.1 BR. If APCR got the restorative postpen buff it deserves, the 75 would become more than competent at 5.7-5.9 (180mm pen and good postpen comparable to 75mm AP) and the 76 at the current 6.3 (230mm pen and 76mm AP level damage).
The game needs to define explicitly what “seal clubbing” is in its context, I feel. Because sadly too many people equate “frontally impenetrable” with “overpowered,” when for too many machines this should not be the case. In the 5.7+ BR range there are too many easy ways to pen something that trades all its mobility for armor (and sometimes also firepower), and for the guns which can’t easily pen whatever they please, the atrocity known as track-and-barrel torture exists.
In my eyes, all this compression is being maintained by 1) continued ease of barrel-knocking even at medium-long ranges, 2) comically low postpen of most high-pen shells (APCR, APDS, HEAT, HEATFS), and 3) incorrect pen/postpen mechanics for many shells (APHE doing too much damage, solid AP often doing not enough, APDS shell shattering on skirts nonsense, HESH doing too little postpen, and HE missing the kinetic portion of its armor-penetration entirely).
How does that relate to the Jumbo 75 (and Jumbo 76)? APHE overperformance makes the gun surprisingly potent, causing screams of it being somehow “overpowered” and thus allowing it to remain at a questionable BR. APCR underperformance means that many opponents which should be able to pen it either outright can’t or if they do they do **** all for damage. The Jumbo’s own APCRs not penning things and doing no damage means the thing is totally helpless outside a complete downtier. Then of course the medium-like mobility of Jumbos means they cannot be placed at a BR where they are frontally immune to most things like the name “Heavy Tank” would suggest. Barrel damage should not be a band-aid for the Jumbo to use any more than it should be for uptiered opponents to use against it.
This is a machine I like to play from time to time, both versions, in fact. And I still make it work somehow by playing it like the medium that it actually is. To truly “fix” the Jumbo would require major overhauls to many interlocking game mechanics.