When I bought 650b wheels for my Giant Revolt late 2019 I didn't pay too much attention to rim width, I just wanted to get a pair of wheels that were well priced which is what I got. I did realize the rim width was 30mm internal when I bought them, but I assumed it would be fine since I've seen other "gravel specific" 650B wheel with wide internal widths (Enve G27, Ritchey Trail 40, Roval Terra CLX Evo).
Actually running tires on these wheels have given a different feel. I tried Gravelkings (Slick current, SK previously), Continental Race King 2.0, Specialized Fast Trak 2.0, WTB Sendero, and Vittoria Terreno Dry. The one thing I noticed is that the only tire that was relatively still close to it's stated width was the Sendero - only the casing stretched out to ~49mm. The rest of the tires stretched at least 3-4mm @ ~35 PSI. The Gravelkings are notorious for being waaaay wider than stated, and these went from the 48mm stated width to 54mm (+6mm). So there comes the first potential issue which is tires being much wider than intended, and limiting tire clearance for bikes with already tight clearance. For me I can run a 50mm but anything past 50 is too risky.
Then comes the second issue I noticed - auto-steer at low pressures. Idk if this is something that bike geo could remedy, but when I was running those lower pressures it feels like the tires will pull in either direction when you turn the bars. I would then add more air to counter this, but then the ride feel becomes way harsher than I'd want it to be.
Those are just my experiences though. That said I do have a narrower 24 mm internal rim that I could replace my 30mm rims with, just that I didn't want to go through the hassle of getting my wheels re-built by my shop. I feel like I should just get them swapped out, but I really want to see if I can somehow make them work a little bit longer. Despite what I mentioned above these wheels have held up and never needed to be trued. They were able to handle my weight when I was still 360lbs so that was great. It's just the little bits of slightly weird handling and having to be super careful about how big my tires will actually balloon to on the rims that has me feeling a bit skeptical of the wider rims.
I have a pair of 700C wheels with 30 mm (inside) rims. I've used 4 different tires on these wheels: 48 mm Soma Shikoro, measures about 51 mm at 30 psi 45 mm Pirelli Gravel H, measures about 49 mm at 30 psi 44 mm RH Snoqualmie Pass Endurance, measures about 46 mm at 35 psi 40 mm Schwalbe Marathon Almotion HS603, measures about 42 mm at 40 psi
I've noticed no handling problems on pavement, gravel, or dirt using pressures from those listed above to about 10 psi higher. You might get a different feel if your point of comparison is a narrower 700C tire due to different geometric and pneumatic trail. I can't say for sure because I've never ridden on 650B wheels.
I also have a pair of 700C wheels with 25 mm (inside) rims which I've used with a variety of tires from 32 to 48 mm. No handling problems with any of those.
I tried wider 700C tires (48 mm Soma Supple Vitesse) on 21 mm (inside) rims and found that combination to be a little unsteady on pavement and very sensitive to pressure. Tires 40 mm and under were fine on those rims.
I don't think you'd notice much difference between 24 and 30 mm rims with relatively slick tires except you can run somewhat lower pressures with the wider rims. However tires with tall side knobs will work better with the tire maker's recommended rim width, which in the sizes you mention is most likely 22 or 23 mm.
I find auto steer to be more affected by pressure than rim width, though it does tend to be more pronounced on wider rims. Add in that a tire at the same pressure will feel firmer on the wider rim compilations the situation.
I run 650 x 47 Maxxis Ramblers on 23mm iW rims. I would be concerned about running them on anything much wider as it would expose the sidewalls to rocks and flatten out the tread too much, increasing straight line drag. They measure 49mm on these rims.
