A text-based tool like this certainly puts a ceiling on presentation quality. Whether that really matters is situational. In most cases, content is more important than style once a certain threshold of "not hideous" is reached.

The same tradeoffs apply to a text-based diagram tool like mermaid.js vs more traditional diagramming tools like Miro.

My coworkers' Miro diagrams are prettier than my mermaid diagrams. But mine are composable and able to be versional controlled. I'm able to create complex diagrams many times faster using a text-based tool.

Ultimately, slides and diagrams are for conveying knowledge. If you're able to convey the same knowledge with significantly less effort, that outweighs the loss of "style points" in most situations (internal knowledge-transfer, meet-ups, etc).