This is a topic near and dear to my heart as I spend a majority of my free time helping other people improve their play for the game both in-game and through other platforms such as Discord - The Balance in particular.

There is a significant spread of skill levels when it comes to the player base and generally, when you help with coaching for long enough through experience you come to know the general goals, plays, and errors for players in particular performance brackets. With this comes the knowledge of ballpark numbers and dps boundaries given various constraints, contexts and factors. I have the luxury of also having worked out and for a long time used the formulae the community use to figure out damage figures and thus dps, so this gives even greater understanding in what can be considered low and high for a given job (my specialty being but certainly not limited to SMN).

When someone comes to the SMN channels for assistance and I notice that they are in fact performing at the lower end I will never call them garbage-tier. Just for recognising that they might be doing things incorrectly and coming forth seeking help with a willingness to learn takes a good deal of courage. Big fan of people like that, it's also why the job channels exist in the first place - to provide assistance to those that want to do better.

However, if someone were to link a clean fight log (no deaths from them) and ask "is x dps at ilvl y good?" I will be blunt and honest with truthful feedback after assessing the factors at hand. If I see horrors in your rotation I will bring them to light with a NotLikeDuck or PaissaSquint, just as I will praise things done consistently and well. The feedback must be balanced and fair.

4k for dps jobs was fairly respectable back when Ala Mhigan gear was the best available and people were still figuring things out (think back to when Susano and Lakshmi were the only raids). We are very far into the expansion now with job mechanics ironed out and lots of gear upgrades later. If someone is more contemporarily geared and as a DPS job are doing closer to or less than 4000 dps then there are some serious play errors happening.

Thus to answer in the context of where the majority of people asking such a question come from in character progression: no, 4k is not good and not close to respectable for DPS jobs at contemporary gear levels, even from i340+ when we consider Deltascape numbers and that dungeon gear is now at i345.

But now more aware, people have a decision to make:

Do they recognise that they could improve and if so, are prepared to spend some time doing so?
Are they content where they are not wanting to change, choosing to remain aware that they are making mistakes but being ok with that fact?
Are they refusing to accept responsibility that they are capable of mistakes and thus see no need to change?

If the first then that's great, there's lots of good resources online and in discords to help you there, not to mention helpful souls like I strive to be.
If the second then that's fine, you're playing the game as you wish to, though be aware in how your preferences can impact the play experience of others.

The only thing that's truly "garbage" in my eyes is the attitude surrounding the third and the tendency to be very defensive, deflect and typically blame parsers and people who parse. There is always something someone can learn to do better no matter where they sit in terms of play ability - regardless of whether the errors were identified with a parser or otherwise.