I hear you on the whiteboard. It's still in its early days. Should be substantially improved in the coming months.
To clarify on mermaidchart.com and mermaid.live, we are the same team. Mermaid.live is our fully open source hosted editor. This was the original editor for our 10 year old open source project. The creator of Mermaid recently founded mermaidchart.com with the CEO of Gitlab's venture studio to expand the capabilities of Mermaid for more users and build an enterprise grade product. The company is open core and venture backed. The Mermaid project will remain forever open source and will continue to invest in growing it and the company for those that desire more advanced business features.
We really appreciate your feedback and support. Ping me if you'd like to chat with our product team about the features you're hoping for:) andrew@mermaidchart.com