That is somewhat true.
You just need a case with decent airflow.
The 3700x is a 65W TDP CPU and I ran it on my Asus ROG Strix B450-F for about a month and a half before I got an Asus ROG Strix X470-F.
And I can say it ran the 3700x (with PBO enabled) just as well as my current X470-F does.
My X470-F has a lot better VRMs but with the 3700x that didn't make any difference when running it stock or with PBO enabled.
I honestly would Not have an issue running up to a stock 3900x or 3950x on that B450-F as long as the case has good airflow.
I'm sure the B450 Tomahawk Max would be a better choice if you plan to run a 5800x or higher CPU in the future due to it's slightly better VRMs.
I can say that Asus consistently offers a better BIOS than MSI though.
And the ROG Strix has been shipping with a Ryzen 3000 compatible BIOS for quite a while now.
IMO either would be a solid choice for a 3700x.
Ultimately it comes done to which board has features the user wants or needs.