To each, their own. But have experienced any benefits from your forum software in Google search ? What if your forum is adhering to the rules set by Google to get into a better position during organic search ?
I don't know because
I was expecting you will say it is Xenforo or IPB. They seems to rule market. Is that without good SEO ?
Their SEO might be good. But how can I say that it is better than phpBB ? More people use phpBB. There is no definitive index or study which we can rely on.
That is a fact. I won't write down phpBB. They do regular releases. Perhaps they keep themselves up to date of SEO rules as well.