This could easily be fixed by paying the creators a much larger per view fee whenever a premium user watched their content. 1cent per view is 10$/cpm, that is 3-6 times more than what ads pay and would strongly incentivise creators to encourage subscribers go premium and create premium-only content for them. Now you can't do that because premium is a ghost-town and you lose ad revenue, but if, say 25% of users are premium then it starts to make financial sense.

Your suggestion to cut the price is unlikely to strongly increase premium subscriptions, YouTube has probably already set it to a revenue maximizing value.