It's not soft at 7mm. It's the automatic distortion correction that can cause it to look a bit soft in spots. I've looked at the same files in DXO Optics Pro without distortion correction and they're tack sharp. DXO Optics Pro also lets you easily dial in the amount of distortion correction you want/need on an image by image basis.As with all UWAs you need to view it as a lens you can't really exploit without the power of the distortion correction tools in LR or CS. I also find it a tad soft at 7 but if you fill the frame then this is outweighed by the incredible effects you can get.
The 7-14mm is a great lens. As for fisheyes, the Panasonic 8mm is nicer than the Rokinon/Samyang, as nice as the Rockinon/Samyang is. The Panasonic fisheye has much better color, IMHO, and is even a tad sharper.