If you look at dpreview, you can download sample RAW files taken with a Z7 and FTZ adapter.
There is one shot of a city at f/1.4, and the frame is sharp edge to edge even at 1.4. I would think this lens blows away the Sigma.
The Sigma is a bit dated, and was surpassed by the Canon 35mm 1.4LII (which I use on the Sony with Metabones adapter). I would say this Tamron is probably even sharper than the Canon, but isn't corrected for out of focus fringing as nicely as the Canon is. The Sigma doesn't match the Canon.
Tamron says this is their no compromise lens. They told their engineers to create the best lens they could. It has a bit of greenish out of focus fringing compared to my Canon (the Canon is like an APO), but looks to be the sharpest 35mm prime, considering the samples I've seen at f/1.4.