You have said it all, a post that's very lenghty and contains no knowledge or be of any help to someone is of no use. Moreover we don't comment on every posts we come across on the form. Look for threads you know you have adequate knowledge about and dedicate yourself there. Some people comments on every posts they come across on the forum, which is not very good. You already know that without quality posts nothing for you.
You’re right on the point you made; people in a bid to get merits go on to write on threads and boards that they have little to no knowledge of what the discussions are about. In a bid to look knowledgeable and perhaps to earn merits, they end up being put on peoples ignore list cause of the misleading or outright false information they keep spewing out.
There’s an active thread aiming to call such users out for posting false and misleading information on the technical board. It’s much better to stick to and contribute your knowledge to the boards and topics you are actually versed in. You’ll still be recognized and merited