You're right because "increase by less" is not the same as "lower." In most situations, building more housing will cause housing costs to increase by less than they would without building more housing. It would take so much new housing to sufficiently flood the market and lower housing costs that no politician would discuss such a dramatic change.

Redditors who don't pay close attention to words think you're wrong because ideology matters more than plain text in the US in the 2020s. It's a shame that so many people feel words first and think about their actual meaning later, if at all.