From the perspective of a CTO, here is what I'll think
- It's a landing page, everyone will see it. If someone looking for a job and find that this company is not using modern technologies, some may not consider it
- We're teaching new dev React, not JQuery. So if there are any edits, even juniors can do it
- Performance wise both React and JQuery are really good. But by default React comes with great tooling (CRA). Like Eslint, Sass support, enforce component splitting, etc
- Use familiar plugins/libs if need in future. Suppose your CTO, as well as others, who are already familiar with React libraries (than JQuery) it will be much easy to integrate
- Longer vision - For now it may seem like a simple landing page. But if future it may evolve into something large
There are many more if you think from the perspective of a CTO. Please don't blame him.