Better ground by what standard?
Depending on what school you train at, it can be accurately concluded that both are primarily throwing systems when it comes to their sport applications.
What cannot be argued is the fact that there are many, many more people doing Judo than Sambo, especially at the elite level. Thus the talent pool is much deeper in Judo.
To further confuse the issue we try to hypothetically determine which player has a better specialized game? The answer is...it depends. There are YMCA Judo Black Belts in the USA and experienced Sambo players from Russia who get tied in knots by one year BJJ students. There are also excellent Judo newaza specialists and Sambo leg lock specialists who are a handful on the mat for anyone.
It simply depends on the school, it's emphasis and of course the athlete him/herself.