So what you are saying is that with the Rigol you simply plug the HDMI into a monitor, and with the Siglent you must buy a PC and configure some software in order to use an external display
No, it's different and let's examine a use case.
Why would we want to port the display when you already have a 10" touch display that's also keyboard and mouse compatible ?
To use the webserver all you need is a LAN connection and a PC on the same LAN with a browser open then all the features are available remotely including of course the live display which then can be used for a larger display or ported to a projector where it might be used in a presentation along with say a Powerpoint window.
All this can be done by just assigning an IP to the scope and pointing a browser to that IP. Same for the SCPI command panel.
Further, additional features are available in the webserver Instrument Control tab as shown here using the same setup I posted a few days back when giving SPI decoding tips to Martin but this time gathered using the webrowser's screenshot button which saves directly to the PC's browser download folder.
Sure this is from SDS5kX and the SDS2kX+ will be little if any different.
Saved screenshot via a browser:
Screenshot of webrowser