Insofar as I might be prepared to agree there is one, I think the real problem with those comments is their canned-ness. I think you're talking about things like the low quality posts review queue comments like...
Please don't add "thank you" as an answer. Once you have sufficient reputation, you will be able to vote up questions and answers that you found helpful.
(uses "please" and suggests a more appropriate action indirectly)
and
While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes.
(uses suggestive, indirect "it is better to..." rather than "you should..." or "please..." or an imperative)
or the close reason messages like...
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
(alas, we sometimes close things as dupes when they are not dupes, and this message makes us look silly...)
and
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.
(makes a polite request and explains the reason for doing so)
These messages use formal, polite language. Maybe when you say "welcoming" you want them to be aggressively welcoming, with phrases like Welcome to Ask Ubuntu!!! But I strongly feel that blog post about being welcoming was not about adopting some kind of servile customer service posture, but mainly about not making new users feel like idiots just because they had to ask a question (what, you didn't know this yourself? Ignoramuses like you don't belong here!). So I don't think "Welcome to Ask Ubuntu!" prefaces to comments telling OP how clueless they are are all that helpful. They just make us sound more up ourselves in my humble opinion.
As you may know, in British English, when we want to make a request or be polite, we become bizarrely indirect, and say odd things like
Would you please [do x]?
Could you possibly [do x]?
If it's not too much trouble, would you mind [doing x]?
These phrases are quite confusing when you think about it. Just getting to the point with a respectful "please" is probably best in an international context. That's the style our canned comments use. No need to embroider.
However, perhaps since that direct formal language isn't natural to me, it doesn't really feel right, and I often prefer to just write my own comment. Writing in my own words feels more sincere. I think users respond to empathy, and empathy just doesn't come through in an obviously-canned comment, however many excess clauses or emojis it has. In fact, I strongly suspect impression-of-sincerity-given is probably inversely proportional to number-of-emojis in canned comments.
That said, I would support an effort to make some of the comments more tentatively expressed, since we make plenty of mistakes in closing and flagging, etc. I would like us, the established community, to come off less arrogant.
You suggested in your question a more tentative version of the duplicate question message, which I earlier said I think makes us look silly when we get it wrong (the real solution to that is to stop closing questions as dupes when they are not dupes, but this is a rant for another meta post, and in the meantime making the message less assertive might make me feel better, if nothing else). The only thing about your suggestion that really bothers me is the nausea-inducing closing exhortation... but maybe a very simple rephrasing would do the job, like
We think this question has been asked before and already has an answer [...]
(I feel the rest of the comment should probably be changed, but the question of what we should suggest OP do about dupe-closure in the close-reason message is probably out of the scope of this question).
