Rarely will you see a quality score higher than 3 if your landing page is not relevant.
As displayed quality score is a 1-10 number; there is no way a bad landing page equates a 10% reduction in your overall quality score.
My understanding is that as long as you’re a legitimate business, not just an Ad Sense spammer, the landing page QS factor is a non-issue provided that the page load speed is reasonable.
Folks who are moving pixels around the page hoping to improve their QS are wasting their time.
In most cases, relevancy is pretty obvious and is rarely an issue as most advertisers don't want to be bidding on unrelated keywords.