I'm no dummy and i know a bit of things, but "enlightened" might be a bit more than i deserve.
Seems like the issue is goes back to what i was saying about the arrangement needing to have sonic space for all the instruments. Even with a wall of sound, walls are built brick-by-brick on the foundation. It's not just a pile of bricks. Longwinded way of saying, they need to make room for the bass in their tone.
Unfortunately, trying to get a guitarist to pull back their big sound could be a futile task.
What it sounds like to me, sitting at my desk far away, not in the room with youse playing is the guitarists are using their "At Home Tone" and not adjusting it for playing with other instruments. When they're at home playing alone, the only thing making sound is their guitar and they can fill up all the sonic space they want. Their guitar sounds HUGE because it's just them and whatever lush, big tone they're using. That same huge tone with another guitar and a bass and vocals (or whatever other mix of instruments) is now taking up all the sonic space and leaves no room for anything else. Sounds great at home, terrible in a mix.
So the guitarists need to pull back a little in the frequencies where the bass is, and the bass can pull back a little in the freqs where the guitars are. I can't say which frequencies are emphasized or de-emphasized for each instrument, because it really depends on the situation and the instruments and what sound you're going for in the song.
And it doesn't take much to make space. You and they don't need to cut all the way out of the EQ. Just a few dB goes a long way. If you're playing a Jazz bass with both pickups 100%, it naturally scoops the mids a little. So maybe the guitars can keep their mids up but take their lows down to -3dB to -6dB? Then you bump your lows and low-mids up tp +3dB to +6dB.
Or if their distortion is big, lush, lows with a glass top, if they're boosting lows and highs aka Smiley Face EQ, have them pull their mids down a touch more and you push your mids.
Whatever it winds up being, everyone needs to pull down a touch where the other instruments are gonna live, and bump a touch where they have their own home. It can be a hard sell to a guitarist because this mix tone will sound worse to them when they play alone. But they gotta understand they're not playing by themselves anymore. They're playing a song, in a band, in a mix.
There's a lot of great info in this video on this subject. You might have to parse it out a little because he's going into a lot of detail about recording and mixing guitars, (and a lot of people are put off by Glenn Fricker), but so much of what we're talking about is in there. About how at-home tone is different from in-the-mix tone, and how guitarists have to adjust their tone to sound good in the mix, not alone. It's true for in the studios; it's true for live; it's true for rehearsal. Pay less attention to the nitty gritty of what he's specifically doing to the tone for his mix, and just look at how he's listening to what the mix need and adjusting, and how he points out where it wouldn't work in isolation, but works when everything is together.
Of course, he's doing that in a studio and adjusting things in the DAW. Youse need to sit down as a band and just do it on your amps & pedals in the room, since you're doing this for live situations. And you gotta get the guitarists to listen to the mix as a whole, not their own tone when adjusting things.
And once everyone has their own little home in the mix so that everything can be heard clearly, you're both supporting and cutting through the mix, because the mix is being glued together and you can hear the bass guitar. And one step further, to "cut through the mix" (as much as i hate that phrase), will only require being a little louder in the mix, or a little louder in your frequency ranges. If everyone has a nice home in the mix, what cuts through and what blends in is just a level balance thing. So, even after all that, what all of this goes back to is arrangement (where everything sits sonically) and "mix engineer" (volume balance, even if the "mix engineer" is the just the band setting their amps to the right level.)
And for an example of this listen to how big and lush the guitars sound in Alice in Chains' "Down in a Hole" and then listen to how brash and thin they sound isolated.
And i say all this not as a bassist who just wants more bass and less guitar, but as someone who's produced and mixed and done live sound professionally.