Buying an Omega or a Rolex etc as an investment should not be a primary reason for the purchase. You are buying the quality, performance and design. If it so happens that you make money on your purchase, great. The timepiece is an extension of you and your personality. So you cant use the investment analogy on this. Unless you are buying a true collectors piece.
The prices of these timepieces will fluctuate. For example, currently there is a worldwide shortage of Rolex watches. They are fetching prices that are over MSRP. Even used watches are bringing more money than new. Once that shortage is corrected. The price will adjust.
When the economy crashed, you could pick up a Submariner for under $4,000. Not you can’t buy them for $7,500. Too many factors to consider when buying as an investment.
With regards to the ranking amongst other watches. I believe Omega is a lot more than a notch higher than the other brands mentioned.