The behaviour you're describing sounds like the user is most likely a troll without a dedicated agenda. He knows where the current boundaries are and how you manage them so he always tries to hit this sweet spot where he is sure to gain some attention while simultaneously avoiding breaking rules.
If this user really is a troll, you should just ignore him. It's likely that his behaviour isn't only apparent to moderators but to the community as well. So long as he doesn't break any rules, you just let him do his thing. Either he fast becomes bored and stops on his own or his doings slowly transition to being a general annoyance for your community. If this happens, your community will sooner or later call him out for not being a nice person and disrupting the community. Often, this is enough to justify temporary actions like suspending his account for a limited time or putting all his comments up for inspection before being allowed to post. All these obstacles will pretty much do their thing and disturb him in his doing, possibly annoying him beyond a certain point where he leaves or learns to participate productively and peacefully.
If he stays on track and keeps trolling, your course of action is: ignore, wait for reasons to sanction and repeat. Don't let it become an emotional thing for you. Be professional about it and be done with it.
If this is a rare occasion where he is actually disgruntled with inner workings of the community, you shouldn't miss out on asking him what's amiss. However, you shouldn't argue with him. Instead of answering moderators need or don't need to be experts on certain topics, you ask him why he thinks so. Maybe he isn't content how complex questions are answered or he misses citations.
The same goes for a community which, in his point of view, is nicer than the one where he spends his time writing stuff like that. (Pretty silly, isn't? I wouldn't waste my time on a community that is not as nice as I wish it to be. So just another sign that he is trolling.) You ask him why he thinks so and emphasize that you like to take every opportunity to help make the community a better place.
Whatever he answers, you just give it to the community and ask for their assessment. Don't comment on it, don't rate it, don't do anything with it. Asking the community how it thinks about it allows you to gauge how relevant his impressions are.
- If they aren't, well, problem solved. You tell him the community largely disagrees with him, nevertheless he's welcomed to further participate to his heart's contents.
- If they are, well, problem solved as well. You were successfully able to find something that's amiss, involved the community and (depending on how your users discussed) already have solutions at hand.
The approach involving asking him what's amiss can also be used if he's a troll. You essentially trash his intentions by turning his emotionally driven comments into a factual and objective discussion on how to improve the community. Most trolls are very conscious about how they are perceived as they want to keep getting attention. By not responding appropriately to your questions, he might just throw all his "build up work" away exposing himself as a brick. (At this point, you can just return to ignore, wait for reasons to sanction and repeat.) Or he responds appropriately and you just gained the upper hand by turning his unproductive behaviour into something productive.
These approaches are written with the community in mind. You don't want to be seen as unjust or unfair - the approaches explored keep this in mind by keeping the community in the loop and extinguishing fire places before they can lit up. Don't get invested and you're good to go, helping foster your community.