If you want to fix this and regain some of the respect that you've lost in the past few hours, here's my suggestion.
Keep the subscription model. Set the non-discounted prices for a year's subscription at the same price level that perpetual license upgrades were. The monthly prices can be higher, maybe 20% more for a year billed monthly than annually. Offer a 10% grandfathered discount to apologize to your current customers for forcing them onto a subscription model. Don't offer any kind of promotional discount on the "all the Jetbrains" package deal - it's already underpriced. I think that this is a reasonable compromise that allows switching to a subscription model without screwing over either old or new customers.
Additionally, be honest. Many of your customers and most of your users are developers. We understand the upsides and downsides of a subscription model from both perspectives. Trying to spin away those downsides will backfire and leave us feeling taken advantage of. You've spent many years building up all this developer goodwill, it would be a shame to lose it over something like this.
Keep the subscription model. Set the non-discounted prices for a year's subscription at the same price level that perpetual license upgrades were. The monthly prices can be higher, maybe 20% more for a year billed monthly than annually. Offer a 10% grandfathered discount to apologize to your current customers for forcing them onto a subscription model. Don't offer any kind of promotional discount on the "all the Jetbrains" package deal - it's already underpriced. I think that this is a reasonable compromise that allows switching to a subscription model without screwing over either old or new customers.
Additionally, be honest. Many of your customers and most of your users are developers. We understand the upsides and downsides of a subscription model from both perspectives. Trying to spin away those downsides will backfire and leave us feeling taken advantage of. You've spent many years building up all this developer goodwill, it would be a shame to lose it over something like this.