Strike Witches isn't bad, but it's nowhere remotely near GuP's level. They are very different though, so they shouldn't be too directly compared, but yeah, GuP is far better, if they must be.
And yes, GuP 12 was awesome and great and I want more of this show. Everyone should buy it so they make a second season.
I didn't watch it while it was airing, but there are certainly people who have watched this who have a fair amount of knowledge of the pilots the witches were based on/WWII in general. There was also lots of specula like one of these images for every episode:
Those are really just references, though, not things integral to the plot like GuP's tanks are. The difference is that GuP is directly about the tanks, while in Strike Witches, any historical references are just passing mentions or visual things that have no actual bearing on the actual series. Strike Witches really pays no attention to historical accuracy, and just tosses stuff in to interest fans. GuP isn't like that.
The SW anime is more like a typical magical girl show with monster of the day plot etc. - just without pants and with WWII references. GuP is maybe the purest old-school underdog-sport show since Taisho Baseball Girls.
I don't know, Saki and Saki Achiga-hen are that as well... though I guess you might call that a little less purely focused on that because of the yuribait/etc. elements? But the mahjong makes up a huge part of the series, and both protagonist teams are very much underdogs, Achiga maybe even more so than Kiyosumi. Saki Achiga-hen is recent and is absolutely in that category of shows.