I’d much rather lose a few lumens after 9 years and have it work but at the potential expense of having to max out the brightness all the time over losing the panel because it came with a cheap AUO or Chi-Mei CCFL display that saved Dell 5 cents per laptop. If this was a CCFL laptop, it probably would have been flat out dead if it wasn’t using a Samsung or LG part. The last CCFL laptops Dell released within the E64XX series is the E6400. This machine is from 2012-2013 before it was replaced by the E6440. Since yours works, it sounds like the LED strip is beginning to reach “half-life” where it works at a reduced brightness. When it happens the first step is to try a new panel, but if that doesn’t fix it then it’s a board driver issue if you have a complete backlight failure. With LED, those failures are less common, even on cheaper displays.
The LED strips do fail, but unlike the CCFL displays where death within 5-7 years was normal with low end CCFL panels.
The E6430 uses an LED panel - not a CCFL panel.