I think it depends on the optic you use on your rifle, as well as the barrel length and profile. The Dominus is a great can but I prefer my Ultra 7 on my 16” factory barreled hunting rifles with low powered scopes over my Dominus because less of it shows up in the sight picture through the scope. I really like the form factor of the Dominus on my target/comp rifles with higher powered scopes and fat barrels.
As far as the 7 vs the 9, I’d choose the 7 for more range use, because I shoot with ear pro anyway at the range, and the 7 works really well while still being fairly compact. I’d choose the 9 for a pure hunting rifle for the extra sound reduction because I would not be using ear pro. Same idea would apply for the Dominus vs Magnus for me.