I get your point, but it's still randomized lootboxes, so that's a hell of a minus. But good to know that it isn't as exploitative as the rest.
Well, it was really bad initially. The original system was that you would rarely and randomly get a loot box with a random item which potentially could even be a duplicate of what you had already (for bulletins this was occasionally ok as they would stack, but having multiple copies of a commander was pointless).
At least now you know when you will get the next box and eventually you'll get mostly coins so you can actually "work" toward an item you would like to buy with in-game coins.
Though I seem to be getting a slight bit of mixed signals, since I looked at the Buyer Guide by A_E and see that USF and UKF would be something I'd play considering those play style descriptions, but the forums here seem to communicate that UKF shouldn't be bothered with.
Well, keep in mind that factions (in particular OKW and UKF) changed considerably over time and guides eventually will be outdated.
What is common to all additional factions is that they were originally built so that they lack certain tools that OH and SOV automatically come with. To some extent they feature non-linear teching and teching all options would be prohibitively expensive. Other tools are simply not available unless you use a certain commander (which often are DLC).
Now, this has been changed over the past year or so, at least to some extent. OKW now has almost all the tools that OH comes with and USF has caught up a little as well. Not much luck for UKF in that respect, though.
In regards of a faction being OP or UP: Well, unless you are a top player, a faction's power level shouldn't affect you much as the matchmaker in automatch is supposed to find you a reasonable opponent with player and faction strength factored in. Also, keep in mind that the strength of certain features depends on the skill level of the players and the game mode involved
UKF, for example, was built around having static emplacements. After some toning down, those are now often considered a waste of resources; you will barely see them in high ranking 1v1 games. However, against less skilled players (and I'm totally one of those), they still could be tricky to deal with and well worth the investment.
UKF in general changed a lot; when they came out, they indeed were very strong mostly due to some ridiculous units or abilities that would totally overperform. For example, the Centaur would almost literally evaporate units in buildings and Crocodiles where close to invincible. Over the last few patches, though, a lot of these extreme units were brought down considerably in terms of performance while the other units got little in return... Still they are probably your got-to faction if you like to dig in around a certain point.