Now coming to actual opinions - I tried to impartially sum up things so far 
Regarding 1, I think this is quite related to Proposal: Consolidating Ansible discussion platforms. If we want to make the Forum the default communication platform for Ansible, I think it is reasonable to expect collections included in the community package to be present on the forum. While it might be “yet another forum” (the “official” forum for a service / product), we want the Ansible forum to be the main entrypoint for Ansible related questions, which often also tend to affect specific collections / services / products. Even if another forum might be a better place for a specific question related to a specific service / product. (Even if only someone replies to a specific question that it’s less an Ansible question but more a question about that service / product and should better be asked in the other forum.)
Maintainers should be subscribed to the Ansible forum anyway for “news for maintainers”, so I think subscribing to a tag that applies to your collection - that doesn’t mean you have to reply to every discussion with that tag! - isn’t that much of an additional burden.
I’m more worried about 2. We have ~100 collections included in the Ansible community package. We already have some issues with collections ignoring (for various reasons, I don’t want to make this sound accusational) our rules. I’d guess that for the actively maintained community collections the authors are probably mostly active on the forum anyway, but then we have a lot more collections on that list. I’m really not sure what we should do here, especially if maintainers actively refuse to take part in the forum. Using this reason to remove a collection from the package seems to be very petty.