Gentrification and displacement are distinct concepts, even if they are usually conflated in colloquial usage. Obviously nobody wants to be forced out of 'their neighborhood' if rent is raised, but this isn't an inevitable consequence of improved conditions. This Vox article does a great job explaining possible policies to mitigate this harm, like building more housing, stronger tenant protections, and upzoning wealthy segregated neighborhoods.[0] As you say, existing residents of a neighborhood should be able to enjoy the benefits of increased investment and improved conditions in their neighborhood.

[0] https://www.vox.com/22629826/gentrification-definition-housi...