Are new users properly introduced to the site when signing up?
IMHO, Yes. (Bear with me).
has there been a large influx of new users this year, who seemingly haven't understood what differentiates a SE Q&A site from a forum?
Yes, although I don't know if the number is any more or less than in past years.
But that's always going to be a problem. We do have a lot of rules/guidelines/nitpicks in general here and across the Stack Exchange sites. That's not a complaint - It's these community guidelines that make us what we are. But it's a lot for a new user to get used to.
But we should start with what a new user does see. Whether or not they read it or pay attention to it is a different issue.
First, they must register to ask a question -- That's not the case on all Stack Exchange sites. For instance, on Super User and Unix & Linux, it's still possible to post a question as a guest.
Before registering, they'll see:
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It only takes a minute to sign up.
When they start to ask a question, they'll see the same help text that we all do:
Title: Be specific and imagine you’re asking a question to another person
Body: Include all the information someone would need to answer your question
Information on off-topic releases
Helpful Links to the On-topic help, How to ask a good question, the general Help Center, and Meta.
Formatting tips (multi-level expansion for each topic)
If they insert an image, a helpful warning to also include any relevant text (new users, less than 20 rep).
Wow! Honestly, I'm amazed at how much the design team has packed in there.
It's based on that viewpoint that I say, "Yes", new users are properly introduced to the site and our guidelines. Adding extra gates probably wouldn't make one bit of difference, and would be off-putting as well.
So how do we handle this instead? (not necessarily addressed at you, but to readers-in-general, and addressing some of the comments on your question)
Be patient. I know that we tire of seeing the same issues over-and-over, but realize that each new-user is, well, new. We may have seen a dozen users make this mistake, but this user has (hopefully) only made it once.
Be welcoming, especially if "correction" is going to come next. I always try to start out with something like "Hello and Welcome to Ask Ubuntu" (something I've seen adopted by a few others), then, "Just a heads-up that ..." (note on what needs work and potentially how to fix it).
Be nice when correcting users. I know that some people hate "boilerplate" comments, and I'm not suggesting that we all use exactly the same comment. But for those of us who often comment, it can be handy to have some "stock nice comments" that can be tweaked for the particular situation.
For the types of "Discussion" questions that you seem to be asking about, perhaps something like:
Hello and Welcome to Ask Ubuntu. While that's a good question in general, it's unfortunately not a good fit for Ask Ubuntu's Q&A style. We're just not set up for discussion-style questions where every answer could be equally valid. Can you potentially reword this to focus on a single, objective question if at all possible? Thanks!
Hopefully the new user sees this as helpful, but some will unfortunately become upset or belligerent at what they may see as "confrontation", even when done nicely. If they don't like the response, point them here for discussion/escalation. E.g.:
I understand your frustration. If you'd like to discuss it further, or with other members of the community, you can post a question on Meta. I don't guarantee you'll get a different answer, but it does provide a place for additional feedback.