Painting would last about the same as drywall. But that is only if you do all the proper prep work first. Deglossing, 2 coats of sealer/primer, then the top finish coat. It also would not look good if you do not caulk all the panel seams, fill holes, etc. Panel seams do not show up on paneling unless you paint. Then they really stick out.
Then, your landlord would have to paint the paneling just as often as any other wall. That does become a huge expense over time. As a landlord myself, I find that nearly all apartment walls have to be repainted each time a tenant moves out. Where as paneling does not need to be repainted at all.
Thus, from a maintenance perspective, it probably is not an improvement from your landlord's perspective. While it may look better to you, it becomes a maintenance hassle to the owner.
Also.....Most leases forbid you to paint or do any renovations without your landlord's written permission. So, should you paint, you stand to lose your security deposit, and possibly more if the damages warrant. Even if there is not a "no paint" clause in your lease, you still would be liable for the damages.