Given that this is posted on his current employers' public forum, I take the "bottom of the ladder" and "not a benefit" juxtaposition as a "ha ha only serious" kind of joke.
There's no way that wasn't intended to have a double meaning.
I think this is the key thing here. This guy came on and grew into the job. He's obviously skilled and motivated, and because he built the systems from the ground up, can keep them maintained with way less effort than someone coming in will be able to.
Even if they find someone who's just as skilled and motivated, that person won't have the key experience of "I built all this" and will have to spend a much larger fraction of time on maintenance/extension.
Ultimately PA will have to hire multiple people to do all this stuff. If they're smart they'll recognize it now, rather than when the smart, motivated person they do hire starts to fail.
From the comment it's pretty obvious this is a two person job and getting a single dev is a business mistake.