I have just swapped the bearings in my RF one. Its a 30mm spindle one so by design has tiny balls ( ). I've put SKF bearings in to give it a go and see if it does any better. The RF ones lasted 1100km, I hope the SKF lasts longer.

My last hope one didn't last loads better and I put that down to it being a 24mm spindle and therefore bigger balls.. circa 2000km before new bearings needed so not worth the £100+ tag for me.

I totally agree sealing overall is the main problem, over loading the 'preloads / slack removal jobbies' generally will put pressure on the seals (or indeed bearings) that isnt needed.
The bearings themselves have a variation in quality of sealing, the RF ones seem to have 'baggy' seals from new whereas the SKF look better sealed.

Hopefully they last longer.

Re Hopes, I lost faith as the bearings were actually wearing out after a year or so. Replacements were more than an XT BB .... Stainless steel bearings have a much lower load rating than non-stainless and I found the hope bearings became notchy after a while. I've had various results with XT BB's it all seems to be down to whether or not water gets into them. Getting it soaked and leave it standing seems a good way to kill them quickly.....

I think I’ve mentioned this somewhere before but I believe there is little difference between typical 30mm external bottom brackets. There’s just little scope to do anything fancy or ground breaking, you can spend ££££,s but it’s still going to contain a relatively small bearing with regard to ball size and it’s going to be close to all that abrasive mud and water. My take is the bearings are a consumable, it takes a few minutes to knock them out of the cups and pop a new set in, good quality stainless steel, ceramic balls just use any contamination to grind the bearing races out nice and quick. If I had the cash I’d be tempted to try a Chris king with the grease injection tool, that said I believe you still need to pull the cranks to use it.

Ultimately I don’t think it’s possible to spend you way out of the short comings of existing bb standards, if I was getting a new frame I’d investigate T47 as I think they allow larger bearings.
Just remember the correct amount of preload is pretty much zero, VERY light finger tightness, just enough to remove play.