[2023] How do Riot decide on the pro meta?

Mandatory pro changes are part of the balance framework (I think this is the most recent dev blog about it, but it's a few years old and I don't work on the Live pod so it's possible there's a more recent post or a more recent version). There are other scenarios where champions are changed for pro purposes (e.g. the framework doesn't suggest champions to buff for pro, only champs to nerf), but the must-nerfs come from there.

Using K'Sante as an example case, looking at top 5 regions, on 13.12 he was nerfed and fell to 70% presence (from 80% on the previous patch). 13.13 saw him drop again to 56% presence, and limited samples from 13.14 and 13.15 have him at 55% and 41% presence respectively. Now, I understand (as does the Live pod that works on these types of changes) that these sample patches running up to worlds aren't necessarily the best data given the way that playoffs lock patches in, but this is the pro data that there is to work with before worlds - it's never ideal, and they have to make decisions about worlds buffs/nerfs with limited information.

Things like Heimer support were nerfed immediately due to skyrocketing quickly to 90%+ presence, though of course there's always debates to be had about how to nerf something that's extremely high presence (and the magnitude of those nerfs) - which is going to come down to trying to balance things like the spectator experience, the pro player's opinions, strategic diversity, etc.

As an example of some of the weirdness that can occur here around pro balancing, historically AP junglers in pro have been in this space where pro teams don't want to invest practice time into playing comps with AP junglers unless they have more than one AP jungler that they see as "op" or "pro playable" because they don't want to invest time into practicing a comp that can be banned out with a single ban on the lone AP jungler they've practiced. So this means that there's a lot of awkwardness around AD sololaner/AP jungler metas where sometimes a moderate nerf to a single AP jungler can collapse the meta as it stands, or conversely buffing one or even two AP junglers can often change nothing at all from a more standard jungle meta. There are dozens of these types of paradigms around what pro teams prefer to play/practice, so there's a lot to consider when the Live pod is looking at buffing/nerfing for pro and there often isn't a clear "right decision" on what to buff/nerf for pro, even amongst people that generally agree on how pro balance should be done.

Now, keep in mind that my understanding might be a bit dated/off given that I've only recently come back to work on League and I don't work on the Live pod that does this type of work, but hopefully this was at least a little informative.