Well i've been on both sides of this subject and i have found that both are equally hard or easy to do. It kind of depends on style here rather than skill.
If you want to draw with lineart then you require a set of skills, without lineart you need another.
I think the reason why people see works with lineart as being inferior to the ones without is because when someone starts to draw something for the first time, they always, with no exception, use lineart. And as artists grow and become better, some stop using lineart, so people assume that works without lineart are more evolved.
Well it's not quite like that. In my personal experience, works without lineart are much easier to do than ones with lineart.
The easy partwhen you draw without lineart is you skip the lineart stage (which is tedious and takes a long ass time) and you jump strength into color. This means you have more momentum. There's little time between the initial idea/sketch to the color/lighting so the idea is still fresh in your mind. You also finish artworks faster because you skip the lineart step (which can take hours). I've noticed a considerable increase in speed after i gave up on lineart. Drawing without lineart gives you a sense of freedom, you're not confined to the lineart. Editing things, even as the wrtwork is almost finished, is very easy.
The hard partwith works without lineart is you have to be bold with shadows. The lineart helps you by letting you not have to use dark shadows to define your artwork, to make it readable, the lineart itself makes it readable. But without lineart, you have to add shadows in order to not have your work be washed out. Rendering things realistically plays a big part here.
The easy partwhen you draw with lineart is, as I've said before, you don't have to think of shadows that much. You can use light colors all the way. You don't have to think of readability that much. You don't have to learn to draw things realistically, but can stylize them however you want.
The hard partwhen you draw with lineart is you have to be very good at design. When shadows and shading don't play a big role in the artwork then the design, composition, ornaments play the major role, and you have to be very good at them. Drawing with lineart makes you focus on the beauty of the line, the way it thickens and how elegant it is, and by the time you're finished, all idea and thoughts of color are kind of stale and distant, i know i used to get lost here. And you also need to have to have a ton of patience because the process is tedious. Another hard thing is you have to be a very good planner, you have to take care of any and all mistakes in the sketch and lineart stage, because editing the artwork in the coloring stage can kill you. If you noticed a hand is placed wrong, in works without lineart you simply take the hand and move it, while if you did a lineart you need to move the lineart, edit it so that it's smooth again, then take the skin color layer and move it, match it to the new lineart, then take the clothing part of the lineart, move that, match it, move any details again, match them etc etc. It's just so damn tedious i used to leave mistakes on, even if i noticed them during the drawing, just because it was too damn hard to edit.
For me, drawing with lineart is harder than without. I'm an impatient person and drawing careful lineart while feeling as the idea of lighting, colors, shadows fading away in my mind doesn't work for me. I did do it for a while, and trust me, there were many works, linearted, half done that failed at the color stage simply because i forgot my idea.
So basically both styles of drawing require different strengths and artists tend to gravitate towards the style that matches their personality rather than their skill.