Look at the Tamron 15-30 mm f/2.8, a fair number of landscape astrophotographers have spoken highly of it. I have not used it. Apparently it is a brick of a lens. My current astro lens set (and general landscape wide angle lens set) is Samyang (branded under multiple names) 14mm f/2.8, Zeiss 21 mm f/2.8 (my favorite), and my day and night workhorse and normal-ish prime Sigma Art 35 f/1.4. But I bought these several years back, and since then there have been many new releases, including the Canon 16-35 f/2.8 III. The Canon 11-24 is f/4, a pity, but if it were f/2.8, the thing would be in the range of the supertelephotos in price and weight.
Plus, there is the ever-growing list of ultra-wide primes, including from some newbies in China. Irix 11mm, Irix 15mm, Korean Samyang improved 14mm f/2.4, Sigma 20mm f/1.4 (!), Sigma 14 f/2.8, etc.
For coma testing, look at lenstip.com, a Polish site, the only one that I know of that posts coma tests (of laser pointer or LED) on all tested lenses. Many landscape astrophotography sites or forum threads will have coma examples from corners of starfield images.