How is a neutral democratic Ukraine a security threat to Russia? Not Putin. Russia.
IMO the best reasonable outcome I see for this war is for Russia to annex the Donbas, and possibly the Azov coast. Ukraine will commit to neutrality from NATO and no missiles, but leave open the possibility to join the EU as an economic partner.
Ukraine is shattered right now. There is no good reason to further seal their fate by handing Zelenskyy to that short arsed madman on a silver platter and turning them into a shithole like Russia.