Yo, I agree, in order to get better lines you need to work on your line quality, so I would suggest you start practicing drawing lines in one motion, let's see if I can explain myself better: usually when inking you have two options:
- Building the line, which is, for 1 line you make numerous smaller lines to form a complete line, much like when you're sketching.
- One stroke lines (what I call one line = one stroke), instead of building it, you make one line using one motion of your hand/wrist/arm/shoulder.
Try to focus your study on inking lines with one fluid motion, that can get you a better line quality. Draw random lines with your pencil and try to ink them with one stroke. Another exercise you can do is to draw continuos lines in a piece of paper, draw horizontal lines all over the page, from one margin to the other (in one motion, again).
All these excercises can be done digitally too.
Finally, another thing I want to mention, I see you put an example of a double page spread by David Marquez, David Marquez seems to ink like you do, I mean, he seems to use some sort of fineliners when inking, he could use a mixture of dip pens, fineliners, and maybe brush pens to fill large black areas (but not to do linework), what I want to say with this is that with the tools you have right now it is possible for you to get such a line quality. But as always. hard work is needed. David Marquez is one of the top artists in Marvel right now, I loved his work on the All New X-men (the example you used, Archangel and Angel, u know). He also works digitally.............
To wrap this up, here's David Marquez's instagram, you can check his line work and the tools he uses to ink traditionally, study him, that's another excersise you can do =]. Fightin'
It is also worth mentioning, that Marvel style inking usually consist of bolder more thick lines than manga, so when inking, traditional artist may retrace already inked lines to get them more thickness, coz u can't get some of that thickness with one stroke of a 0.3 fineliner....................... So you get a mixture of building lines and one motion lines... ok I'll stop now....