No, it also works when non-optimal designs are very common in the market. (Not helped with the fact that especially in electronics many brands have decreased in (perceived) quality, so even if something performed well people don't necessarily trust that newer versions are too, which makes actually good brands also less sticky)

I don't understand.

Bad brands aren't sticky in this situation, are there. (I don't know whether good brands are sticky here.) So there's no extra incentives for planned obsolescence, because the next purchase is more than likely to go to a competitor.

Or what do you mean?

They’re saying all brands use planned obsolescence to force consumers to buy lightbulbs (from any brand) more often, increasing sales for the whole industry, not one specific brand.

This is how the Phoebus Cartel worked for incandescent bulbs. Every brand was in on it, it wasn’t about improving market share for specific brands.

That requires a lot of coordination. Any single company could break ranks?

There's a mechanism: if people want their bulbs to match, they might pick the same brand/model as a replacement