My personal experience tells me that there is a good reason why Heinlein takes more focus on this comparison.
It goes without saying that I think some of these comparisons are not fair and this included; though as contemporaries the certainly have some common ground.
The first Poul Anderson I read was After Doomsday.
I was eleven when it was published and maybe twelve when I read it. I bought it because of the space-suited alien with bug-eyes on the end of stalks that hovered around its helmeted head. Wore this one out and recently found a copy of the same date and now have that.
My first Heinlein was Starman Jones
which was published in 1953; however I didn't read it until the 1967 dell edition--once again purchased for the cover. Still have this book
Though read much later--there is no doubt that my influence comes from Heinlein.
I had the book club edition from 1961--I still have it.
Stranger in a Strange Land is a best-selling 1961 Hugo Award-winning science fiction novel by Robert A. Heinlein. It tells the story of Valentine Michael Smith,...
www.biblio.com
I think I read all of the Juvenal fiction he wrote at about that time. I'm certain that it was all heavily edited and possibly his Stranger in a Strange Land might have in part been a knee-jerk reaction to frustration.
However if you want more factual evidence on that read the biography
Amazon.com: Robert A. Heinlein: In Dialogue with His Century, Volume 1: Learning Curve (1907-1948) eBook : Patterson, William H. : Kindle Store
www.amazon.com
Rather than continue spreading my miss-information. Have this on my shelf (Well worth the cost if you are a fan.)
Any way the point here is that Heinlein's Juvenile books gave him a young audience to grow up with and I think that that is something missing in Poul Anderson's port folio.
I think I read all the Heinlein's Juvenile editions and a few others well before I read a second Poul Anderson novel.
However, it should be noted that In the mid 1960s I was limited to the school library and every drugstore I could reach on my bicycle. Though, I confess to having ordered a number of books directly from the publisher back then.