"Do raised beds prevent disease better than in ground?"
no

I prefer to grow some veggies like lettuce, spinach and other greens in raised beds but really deep, wide rooted crops do better for me in the ground so I do both. This did require that I had to be creative with my drip system but it's working great now.

In zone 2, I go for raised beds for warmth-loving crops in summer and for all crops in spring, and I use in-ground beds in fall.
I guess raised beds can indirectly prevent some diseases, mostly fungal, by being warmer, well-drained, allowing roots to use their natural defenses more effectively, but nothing is guaranteed. It all depends on your climate and crop. I guess the only two potential downsides of raised beds are that they dry out faster and are a pain to construct.

We used to have a community garden plot on low section of a dried up river bed,
so when we got too much rain, our plot went under water.

Raised beds did help a lot with disease under those circumstances.

My vegetable garden has always been in ground. I considered doing a raised garden this year after binge watching YouTube videos on square foot gardening. I just felt like the start up costs for it seemed so high, and I had nightmares of weed eating around 9 raised beds once a week haha!! So I stuck with my regular plan this year. Disease is the same regardless. I do think raised beds would be better for weed control, but I bought an electric tiller this year and planted everything in such a way that I can till between everything, so my weed control is so much easier now and only takes 20 minutes to do my large garden. I don't use anything but dirt in my garden. No bug control, no growth supplements, Miracle Grow, fertilizer, nothing. I get great results here in west central Illinois zone 5 with almost everything. Good luck!

I didn't do raised beds, I just plopped it in the ground.

I wish I'd done raised beds, and next year when I open another part of my yard to gardening, it will be raised.

My problem now is, my artichokes are in the non-raised bed, and I'm stuck with that until they run their course (3-4 years).

I wish I'd done raised beds just for the convenience of maintaining the garden. :)

I think raised beds can offer better protection against root rot or other opportunistic infections caused by soggy roots.

I only do raised beds (1) in a place in my garden where plants would probably get washed away every year by rain runoff (my strawberry bed), though I may build a diversion dam between a downspout and my garden next year.

The rest of my garden, I grow on raised rows, for drainage insurance, and less severe bending over for planting, cultivation, and harvesting, and better containment of the grass clippings I use to mulch the space between my growing rows.

Raised beds can help with diseases with a soil mix that provides superior drainage. Even better put a soil less mix or use pots to cut down on diseases. The best defense against disease is healthy plants. If you can grow healthier plants, you'll have less disease. This is easier to do in a raised garden bed. It's also easier on the back and knees to work with.

We have long, wet springs, so our new garden is done in raised wide rows - no sides, just the rows are shoveled higher than the paths. Of course, we also have long, dry summers, so the muddy paths are going to be a waste of water if we don't switch to drip or soaker hoses at some point.

I have a 40x40 side yd garden that is heavy and has a lot of clay but I have tilled it for 35 yrs now. I grow corn, beans, tomatoes, cukes, kohlrabi, leaf lettuce, squash, green onions, peppers and eggplants. It grows most of them very well. Not bell peppers however and the eggplants are hit and miss. I am growing those in the 5-1-1 and they are thriving. I have two Black Beauty EPs in a large 18 gal tote that have 12 fruit right now. The Estler Mortgage Lifter tomatoes in my garden are plentiful and huge. Some weigh 24 ounces. I do have blight in my soil but I refuse to spray Daconil. I have 65 tomato plants and will be satisfied with what I get. 13 of those were Dixie Golden Giant, Omars Leb, Mexico, Giant Belgium, NAR from seed and transplanted about June 15. Hoping those produce late fruit. I couldnt see any reason to invest in raided beds.

I have both raised wide beds [unbordered] and flat areas that I ridge some to make dryer in spring because of heavy spring rains. They both are great.

I plant on raised bed because of the advantages describe above[previous posting ]. I staple my plastic mulch on wood that lined the bed

We use grass clippings as a mulch in the raised bed and around it. No need to weed wack. Just a few weeds poke through. I prefer the old fashioned style garden. This was hubby's thing. It is easy to weed and to pick the crops because it is only 4 foot square. That's the only advantage I see.

I have 9 raised beds, mainly because it is easier to protect my crops in them. Otherwise, the open part of my yard is exposed to a nearby canyon - filled with lots of critters - skunks, raccoons, recently noted rabbits, squirrels, rats, etc., etc. It would be difficult to build a fence because of the sloping nature of the property.

The beds are protected with PVC type pipe cages with chicken wire surrounding - none of the above critters can get in. Yes, it takes a little bit of effort to construct this type of set-up, but I have good crop yields, and it has been well worth it.

I try to grow a little bit of what we like to eat - but not entirely, so small size plots - a little of this and that - are ideal for our family. It's surprising how much can be grown - although our climate is year-round anyway, so these box-type planters are in use all of the time.

Bejay