The Sony 12-24mm f4 G FE is designed to compete with the options from Sigma, Canon, etc. So why would Sony design a lens like this, you wonder? I wondered the same, exact thing--and then I saw it and held it in person.
The Sony 12-24mm f4 G FE is incredibly small and for the first time, I'm very glad to say that Sony has made a zoom lens that doesn't make me cringe in terms of size in relation to a mirrorless camera. It's also go weather sealing built in though Sony says that it isn't to the spec of the G Master series. . thephoblographer.com