Actually all Japanese carriers suck balls.
Let's see...
1.) No shared data plans. You have an iPad and iPhone you will need to pay for two separate plans. You will actually get two separate invoices in the mail/email.
2.) Zero unlock support.
3.) Give a separate marketing title to real LTE and charge as a special service separate from 3G.
4.) When sending photos via SMS/MMS be prepared to wait up to 1 minute for the photo to finish sending. If you send 3 photos in the same SMS/MMS be prepared to wait up to 3-5 minutes for the message to complete sending.
5.) Inconsistent accounting.
6.) Staff that can't tell their ass from their head.
7.) Hardly any free WiFi spots even in the biggest cities. Mostly subscription services from NTT, YahooBB, Docomo and other 3rd party global WiFi providers.
I'm certainly no fan of the carriers here in Japan I've complained about Softbank quite often in these forums but I do feel you're overstating the truth.
1) While it's true there are no "shared" data plans for the iPhone and iPad, you can set up your account so that both plans are invoiced together. Contact your carrier, and they'll have it set up in about 5 minutes.
2) NTT DoCoMo (they are one in the same) allows unlocking and unlocked phones, and supports them.
3) Not quite sure what you mean by this. DoCoMo and Willcom both make a clear distinction between 3G and LTE, and offer distinct plans for each.
4) The speed of network services obviously depends on both the location of the user and, ultimately, how good the network is in the first place. I've had both outstanding SMS and MMS transfer speeds, and horrendous ones.
5) If you've had problems with your bills, then you should contact your carrier and demand a correction. I've never once experienced an accounting error on any of my cell phone bills (I've used DoCoMo, J-Phone, Vodafone and Softbank), and I haven't had any family or friends tell me of any such trouble, either. I'm sure accounting errors occur, but I haven't seen evidence of such errors being widespread.
6) I've experienced nothing but outstanding customer service from DoCoMo. Softbank customer service has been inconsistent for me, but several times it has been excellent.
7) Softbank's WiFi network (free to iPhone users) is among the most extensive and best I've experienced anywhere in the world.
I've posted this not to challenge you I don't doubt you've had lousy experiences with Japan's cellular carriers, as I've had bad experiences with them myself. But I've also had many positive experiences with the carriers here, and wanted to point them out.
Cheers!