Well, it looks like the Groups.io page for the messages in a given group, using topics view, is best and most efficiently read using the links list.
Once the links list is up you can use D three times to get to the date link and it's always three down arrows from there to get to the list of links that are interspersed topics and the user profiles of those who started each topic. What I find most interesting is that once I open a topic, any topic, and use the backspace key to go back to the topics list page I can use up and down arrow to move through the topics/profiles (I wish I could avoid the profiles, but they're links, too) links using up or down arrow just as I would expect I could. What I have not been successful in doing is getting NVDA to throw focus on to the first topic on the page without using the links list, getting to the Date link, then down arrowing three times to get to that first topic. I can't seem to tab to it at all easily.
Once any given topic is open I can take advantage that Groups.io includes a message number link that begins with # just prior to the message text. You can keep jumping forward to the next number sign character to get yourself placed just prior to the actual message text once you've listened to the actual prior message, or part thereof. It's a lot faster than listening for the reply, like, more, and additional links announced before the next message number link.
It is true, though, that in order to efficiently read virtually any online forum you'll have to have someone who can actually see the way the page is laid out, e.g., that message number link, to set up a plan of attack for future reading. Obviously, this is not ideal.
There are subscription options that can only be configured via the web interface in the Advanced Preferences on any given group's Subscription page that can greatly decrease the amount of e-mail you get but still lets you get a sense of what's happening on the group. The option to change Message Selection from getting all messages to instead get only messages for topics you're following, coupled with the checkbox with it to see first messages in any new topic as well, can cut down hugely on the volume of e-mail one receives from a given group.
There is also another control related to Replies, which will automatically follow any message you either start yourself might reply to the first message, which pairs nicely with the above Message Selection criteria.
These settings also work in conjunction with digests if you're getting digests rather than actual individual messages. They also work with Mute Topic so if you do choose to mute an individual topic, even if you were following it, you'll see no more of it.
There are just a lot of things that are too complicated to come up with e-mail control messages to set and unset that are available only via the web interface to my knowledge.
Life is the art of drawing sufficient conclusions from insufficient premises.
~ Samuel Butler, 1835-1902