Sure. I was mainly concerned with the idea that most people are dating for marriage which I don't think is the case, at least under age 30.
But I think it's possible to be a relationship expert even with one or two real relationships. Two sets of people that have been married to only one person are not necessarily equally happy or fulfilled. A person could also make relationships their personal interest and spend a lot of time thinking about the topic on top of their lived experience which might make them more capable of giving advice.
I think it's wrong to say anyone giving advice isn't worth listening to.
If instead you had 30 relationships, whilst for sure you had a lot of experience, I wouldn't really trust your advise as an "expert".