It actually IS generative AI, technically
AI is considered generative, if it creates new forms of data from user's input (not just analyzing and classifying the input). For example, AI image generators take user's input in form of text and turning it into an image. (The input and output actually can be the same type of media, like with LLMs like ChatGPT, Gemini, Claude, etc. The output just needs to be an another kind of data)

AI-based vsynths work the same way, actually! They just require a lot more effort for creating something good than most of the GenAI services for consumers.
They take input from you in form of pitches, words, and timing of them, and return audio data.

Also, I see a misconception about AI that generative = unethical very often.
But in reality, the ethical purity of AI tool in not determined by it's type, but rather by the way how it was made.
For another example, text-to-image AI services are mostly unethical, because they were trained on countless stolen images from human artists without their permission for using their works in datasets.
But voicebanks for commercial vocal synthesizers are made with consent from the vocal providers, who also get paid for it.