While I understand the need to restrict nefarious activity on your API, there is no real migration path for existing devs to Helix. Helix remains a fairly barebones “replacement” for the functionality v5 provided. Development of it has been slow to almost non-existent over the past year, and many developers just keep waiting to switch because of this. Scopes cannot be “upgraded” to Helix without re-authorizing all users, and much of the niche functionality (which Moocat alluded to above) my bot also uses is missing in Helix too.
It is fairly disappointing to see this kind of stark action coming from Twitch. Before you bring up walls around the old infrastructure we all still very much rely on, it would be great if there was a solid feature/migration timeline for Helix in place first. The deprecation timeline of less than a month for these added (imo harsh) rate limits is also quite concerning.