Wouldn't this sort of be a prisoner's dilemma sort of situation? The cartel hinges on every producer being complicit, if they are they get all long term small advantage, if they aren't, they and they alone get a huge short term advantage to the detriment of everyone else.
If a single one of them doesn't play ball and start selling "forever lamps" that last a hundred years (slap some patents on running LEDs at their rating, why not), they'll effectively salt the earth for the entire market.
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)
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.
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.