The Importance of First Impression in PhD Applications
In the US, few entering students have much in the way of research. The usual case is that students enter doctoral programs without an MS or the equivalent. The earlier education is broad, not especially specialized. So, in the US, lacking research credentials should not be an impediment, provided that other things in your background point to success. 

The situation in Europe is quite different as the undergraduate program there is more specialized. I'll let someone with more experience there answer for the EU. I suspect, however, that a few papers would be looked upon favorably. 

But the path may be longer in the US, with some coursework prior to qualifying exams. Five to seven years past the BS is fairly typical, with the early part, again, not particularly research oriented. There are exceptions to this, of course, and it is possible to enter at a more advanced stage as long as you can pass the exams and find a suitable advisor. 

And note that in the US, it is relatively uncommon that you enter knowing who your dissertation advisor will be. That choice is normally made later after you have narrowed your field. So a "first" impression with the advisor depends less on your CV at entry, and more on how you do in the first years. 

But the question you actually ask (mediocre, first impression,...) is more subtle. You need an excellent CV and Statement of Purpose along with letters of recommendation. It is just more likely to be light on research in the US.