It's not about security through obscurity but "if a measurement becomes a goal then it ceases to be a good measurement" - so keeping the measurements hidden in order to make it harder for them to become a goal is a decent way to go on about it.
How would you measure "without ads"? That would just be the same cat and mouse game that adblockers have to deal with for decades.
I'm not sure it's possible to find a good completely open source solution that's not either giving bad results by down rating good results for the wrong reasons or that's open to misuse by SEO.
That might work if it's a small project where noone cares about fixing the results but if something like that becomes mainstream it's going to happen