I'd put it 60-40 at worst, 55-45 for stages like Castle Siege/Battlefield where Pit's camping tools are mitigated and Side-B to get rid of bombs is easily punishable. Not quite as bad as you'd make it. Not to mention Pit doesn't have the best tools for getting BBM horizontally offstage since a lot of his best moves hit up to a degree.

Pit can jump away from bbm tho, and large stages are also worse since bombs can be avoided easier and can potentially allow circlecamping that Pit can do with his 25 jumps and all the arrows he has in his disposal

Also, when pit can just press "special" and he can basically mitigate the usefulness of 3 of bbm's specials, a "Down + Special" that can nullify any projectile that isn't from above (although pit has great aerials too), and any bomb set on stage can be removed easily anyway in the case that making them hurt the user instead is unviable

Although, what exactly can a BBM do against a Pit that spams controllable arrows?

You severely overestimate the effectiveness of Pit's tools. Yes, arrows can be challenging, as can Side-B and Down-B. But they are not without faults.

Down-B is circumvented by bomb throw's trajectories.

Side-B is telegraphed and leaves Pit open; if he's hitting bombs, he's not hitting Bomberman.

Arrows can be challenging, but Bomberman has terrific ground/aerial speed and aerial control. If Pit wants to camp all day, we have solid normals to get in with and combo him.

Beyond that, Bomberman has a really easy time edgeguarding Pit due to a linear Up-B/Side-B recovery. And a lot of Pit's combos are subject to good DI, lending Bomberman some high survivability unless Pit can carry him horizontally, which strong vertical DI can avoid at higher percents. Pit doesn't have the greatest kit for carrying opponents horizontally, either. Instead focusing on a very strong Up-air which kills later on a heavy Bomberman. Meanwhile Bomberman can kill relatively early with P-bombs, Fair, Dsmash.

Pit has good combos and edgeguards, but outside of solid reads, Bomberman can be a hard kill for him, and you can only deal with so many bombs before you get punished for telegraphed responses.

Pit can challenge said aerials with disjoints though, and pit also has better air game overall

P Bombs can be easily reflected by down b or clanked by neutral b depending on whether it's grounded or airborne, and pit can still interrupt charging of bomb with a simple arrow

Bomberman shouldn't be spending all his time throwing P-bombs, especially in that kind of a MU. Only in an edgeguard or if time permits while Pit is airborne. Otherwise, small and medium bombs all day to pressure Pit's limited aerial and ground mobility, forcing him into predictable special options to deal with bombs. Pit's lower speed relative to Bomberman makes it easy to play hit-and-run, making Pit's air power less potent as we can space bombs, aerials, etc better than he can.

But Pit can still shoot your bombs though, unless it's a star/screen KO, that's just one small bomb advantage

And Pit has better aerials overall, really

FAir and NAir autocombos really well, while BAir is a great spacing tool

Not to mention, Pit can still cover the ground pretty well especially with Dash Attack being a really quick vertical launcher and can catch landings very easily

Another one of BBM's (or any high faller, really) weaknesses is their easy to combo status which is a huge downside specially when Pit already has great combo tools

I will shift to speaking from experience rather than on-paper in the MU. Nair is definitely subject to DI, moreso than Fair. With dash attack covering landings, Bomberman landing with bombs breaks a lot of these combos and can interrupt a lot of Pit's rather long multi-hit moves, effectively putting Pit at a disadvantage just because his moves take a while to hit the knockback that matters. Despite BBM's combo status, Pit can really struggle to kill him without edgeguards, and his upwards trajectory off a good number of moves doesn't help that cause.

Pit has good tools against BBM, but dude, 75-25 is giving Pit way too much credit in the neutral and with how effectively he can negate bombs. BBM's at a disadvantage, but a strong BBM player will maximize superior ground/aerial speed and traction in neutral, utilizing bombs in situations that Pit cannot easily mitigate, and ensuring good upwards DI to minimize the edgeguarding game.

Honestly, Pit's best strategy is like v0.9b Sheik: get a ledge kill at like <40% from gimps, or risk letting the stock go to 130%+ when a good read can end it. Plus the MU is very stage-volatile, which makes it further up-in-the-air as to how this thing plays out. But in general, a smaller, platform-driven stage is BBM's best friend in making boms super annoying.

<-- you want this dude to cover the half of FD or similar stages to it? Just place a bomb below you on the stage, make sure it's directly below you. Now charge a bomb, jump and place it below you while in air and kick to kick not only the bomb you placed below you, but also the bomb you placed on the ground, making it either an easy KO or easy dmg farming..... to a kill.....

(please let's get more techniques and tips)

They removed the hitboxes off of the thrown bombs?
Bomberman practically lived and breathed off of those to start combos.

Weirdly enough, he was still high tier in 9b even without those hitboxes

But some of his bad matchups were much better for him because there was a hitbox. Being aggressive was a safe option then! Now I have to constantly run away again.

bbm was good in 9b because of his uncalled for mobility.
Bbm was ok in beta because of bomb throw->explosion
new beta doesn't have either. so it sucks to be bbm

You forgot the busted hitboxes on key moves and the crazy KB he just had. FThrow anyone?

At least he has his kill options back, but now the aggro players are scary again.