I see there's still a great deal of misinformation going on in this thread.
The simple version is that, even if the number of megapickles is exactly the same, the larger format will intrinsically produce sharper images.
I'm attaching an image to demonstrate this. It's a simple enough experiment that anybody can perform: set up a still life. Take two images, one with a long lens and the other with a wide lens -- or with a zoom at either end of its range. Crop the wide image to the same field of view as the telephoto image, and scale the two to the same pixel dimensions. You're left with two images with the exact same number of megapickles, and everything else is either constant or can be controlled for. The sensors of the two images is identical, so you've got the same S/N ratio, the same everything.
To do the most fair comparison possible, you'll want to use the same shutter speed for both images, an aperture sufficiently smaller for the telephoto to match the depth of field, and an equivalent higher ISO to keep the exposure the same. That's exactly what I did below.
And, you can clearly see: the image generated with the larger, 135 format sensor is significantly sharper than the image generated with the smaller, P&S-sized sensor. And, again, I stacked the deck against the larger format in every reasonable way I could.
Pixel density is important, yes. But so is format size. For the absolute best results, you'll want the highest pixel density you can get in the largest format you can get. But, if you have a choice between two cameras of different formats and different megapickles, go with the bigger format. (With, of course, the usual caveats that sufficient technology age can skew the results.)