Well, you didn't mention anything about winning majors which isn't really what being consistent is about anyway. The fact remains that between winning Wimbledon in 2013 and this year, Murray had reached three other Slam finals as well as three semifinals. Apart from Serena, which other player on the WTA has had anywhere near that level of consistency in recent times?
No one on WTA is as consistent as Andy, save from Serena. But no one else on ATP tour is nearly as consistent as Andy, either (excepting Novak, obviously). Who's the next most consistent player after Andy and Djok (I'm leaving Fed and Nadal aside since injuries have been ruining this season for them)? Stan?
I don't think anyone would deny that there's a bit of a consistency issue in the WTA overall. But I think it's massively overhyped on this board. To read some of these posts, you'd think half the top 10 has had exactly one good result in the course of their career.
Muguruza mucked up this Wimbledon to be sure (though her presser left me with the impression that she had come down with something viral; looked completely lethargic and without energy). But she has two GS finals, a WTF semifinal and finals of two strong tournaments from last year's Asian swing. Hard to say the FO trophy was some sort of a flash in the pan moment for her.
Radwanska seems more consistent this year than ever before. Captured at least one title, got to SF at AO. Eliminated in the fourth at FO through a bit of bad luck (was firmly in charge of the match and would almost certainly have won had rain not drastically altered playing conditions). The fourth round at W is doubtlessly a disappointment, but she was at least eliminated in an epic, high quality match by an on-fire top 20 player. I wouldn't call that embarrassing.
Angie backed up AO with W final. Also has a title from earlier this year and Miami SF, iirc. An up and down season, to be sure, but it's not like AO is all she's achieved. And her conqueror at FO went all the way to semis, where she put a solid fight against Serena, so it's not like she lost to someone who couldn't find their way on the court in the next round.
Venus reached QF of the last USO, won two titles after that. Got sent home at AO in the first round to be sure, but Konta made it all the way to SF, so I'd say she backed up that upset pretty well. Fourth round at FO where she lost to Timea is pretty respectable, given that clay has never been her thing. Semi at W is awesome.
And so on and so on.
The girls lack consistency to a degree, there is no doubt about that, but it's not as though decent results are ridiculously few and far in between.