While I have not seen the MSO5000 in person, I have read some report of a dim display, and thought I would share some opinions and ideas with this fine community.
It appears to me the display used in the MSO5000 is based on TN technology, I have a computer monitor that is TN based, while it has excellent refresh rate and response time for gaming, the viewing angle is terrible as evident in Dave's video when he tipped the unit backward. The contrast simply disappears when you view from an angle. While increasing the backlight LED brightness may help to a small degree, it will only lead to higher backlight bleed-through and will not at all help with the viewing angle. Since we may move around the bench and not always right in front of the scope, this can be a issue with some people.
OLED has excellent contrast, but it has issues with burn-in at high brightness with static images, that to me would make it less optimal for scope display, items such as the Rigol logo would surely cause burn-in over time.
That leaves IPS the best compromise in my opinion. The cost of IPS vs. TN is not that significant, the screen being the most crucial interface in a scope, I am surprised that Rigol did not go with an IPS display for the MSO5000.
I had worked with screen readability on computers in my career, when there is a hardware limitation, we try to compensate it with software. In this case, I am shocked to see numerous colored text in the UI against a dark background . Those would be marginal even in an OLED display, and would look awful in a TN display. We had learned to not use red or magenta text in our designs. If software development is not tightly coupled to the hardware team, it is easy for them to go off and development a pleasing UI using an emulator on a big IPS computer display, but when you run that in a small TN display, it results in a poor readability. This can be improved in firmware by using high contrast text, make all active text white and using the box around it to show color if needed.
Even better, switch the display to IPS, it will make it really pop against a black case.
Interesting, when I look at some of the Rigol demo videos of the unit, it appears they capture either directly through the HDMI output or on an external monitor. Rather than from the actual display of the unit.
I do have one question for the community, does other scope from Siglent, Keysight, Tek, RS, etc... have this viewing angle problem? How about units like the Siglent 1204X-E or the SDS2104X?