Outboard bearing bottoms bracket (hollowtech II) - assessment of wear and lateral play, lifespans & when to replace?
That there's some amount of play you can feel through the black plastic shield in one of the bearings with the cranks out isn't necessarily a big deal. What you're looking for is the quality of the adjustment you can get out of it with the cranks on. If you're forced to either have it grindy/frictiony or have play or both at the same time, that's a BB that needs replaced.

Broadly speaking, yes you seem to be wearing them out on the fast side. Your description of the issues you're having somewhat suggests not enough care given to keeping the bearing adjusted. You shouldn't have to mess with it all the time, but every once in a while on a Shimano outboard BB to be sure. You're trying to always keep it slightly preloaded. Another way of saying it is as loose as possible but with no play. Too little or too much preload will trash the bearings.

Chronically running through these BBs, especially despite ones best efforts with adjustment, can also suggest a shell that needs facing and chasing to get better bearing alignment.

Outboard BBs, the cheaper ones in particular, really aren't all that durable compared to high quality square taper cartridge BBs. I have a BB-UN72, Shimano's nice but modestly priced upper end square taper unit, with thousands of miles on it in all weather conditions and over 10 years old that's still utterly perfect. No outboard BBs do that that I'm aware of. 

If you're doing high mileage touring then just getting a King or Phil along with making sure the shell is well-prepped would probably make some sense. What kind of mileage you get still depends on you and the conditions you ride in, but they are more robust. I'm also a big fan of the Enduro replacement bearing kits for Shimano outboard BBs, because they replace the bearing with a larger and more durable cartridge by getting rid of the black top hat seal and putting a different kind of seal in its place, but the catch with them is you more or less need a special tool to install them into the cups. I've observed them be a good solution for folks having trouble with tearing through BBs though.