IRC simply a different use case than a forum. I think both are useful and I don’t see a reason why a company couldn’t have IRC and a forum, there’s no contradiction and the overlap is small.
Forum are very useful for example for use cases where the topic is extremely specific and you throw out a post “who else does this and have this issue?” and hope someone will find your post through internet search and the more people find the thread the higher the likeliness to find a solution.
IRC is nice for quick back-and-forth type conversation for topics which are more “common”, where the requirements to participate in teh conversation are lower. For example, a discussion on a potential feature request.
Forum are very useful for example for use cases where the topic is extremely specific and you throw out a post “who else does this and have this issue?” and hope someone will find your post through internet search and the more people find the thread the higher the likeliness to find a solution.
IRC is nice for quick back-and-forth type conversation for topics which are more “common”, where the requirements to participate in teh conversation are lower. For example, a discussion on a potential feature request.