Let me actually lay out this argument the way I see it:
Omega Mode is nice. It makes all the stages FD, and it's nice to not have to listen to the same theme every time we play. But the issue is, it's ONLY FD.
Whether you play competitively or not, FD is not a fair stage in all regards. It does heavily favor ranged characters. With the buff to dodging, and the lack of platforms, it's easy to stand on one side of the stage and use projectiles to force your opponent to approach a certain way. And with the lack of room to approach, your movement is easily telegraphed and easy to abuse. Most projectiles have been nerfed, yes, but some are still very strong, like Bowser Jr's Mecha-koopas and cannonballs.
In the competitive scene, FD is rarely played on. Ground based characters have a decent advantage compared to other characters, and with the ways picks and bans go, FD would often get banned. (I got this a lot as a Diddy player, Snake and IC players would be the same).
There should be a few platforms, even if it's just three stages, (BF, SV, FD) It's enough variety to give close range characters a chance to actually get in. To those of you who aren't competitive, don't say that this is us crying about something we wanted. Smash is beautiful hybrid of being fun for casual AND competitive play. So many people think competitive just means "No Items, Final Destination, Fox Only." It's not, and in fact, in Melee, Fox is considered to be at the disadvantage on FD against Marth due to the chain grab.
To the competitive people, it's not bad, it's nice to have a mode without any gimmicks, I wish there were a few platforms as well, but at least we have a mode for ourselves. It's not that it ruins competitive play, it more ruins the meta. Some characters will be ranked pretty highly just because it's on a flat stage as opposed to having platforms, and most close range characters will be lower on the tier list. Keep in mind, Japan ranked Pit like 4th best in Brawl, but they only play on 3 stages, in NA we ranked him very low. If you're having a tough time with it, it sucks, you'll just have to use characters that are better on flat stages, which sucks cus you're now more forced into playing certain characters, or we can try to make our close range work.
Just my thoughts on the matter.