There is little difference in IQ for any DSLR at ISO 100. You are buying features and hype.
For landscapes, more MP will give you more detail, but as MP count goes up, so does the difficulty in actually getting that extra bit of resolution. There are some who do very well with high MP cameras, but the average photographer is not obsessed with a incremental increase in resolution, the more important elements such as composition and subject, lighting, DR, etc put and IQ improvements far down the list. In fact, I don't even know how to measure something hypothetical like IQ that only exists in the mind of a photographer and is different for each of them. We can measure several parameters, and they trade off against each other, but IQ? That sounds like something DXO would assign a number to