Oh, I do think the MK match-up is bad enough that picking up a secondary (or new main if you think MK is really
that common) for the match-up is probably a better plan than trying to fight the uphill battle.
(Personally, I've subscribed to the philosophy that you should pick a lesser-used character, i.e. someone besides Snake or playing the MK ditto, such that the opponent is less likely to have significant experience with the match-up.) However, it's not "hopeless" to the point that it's nearly impossible to win and one could probably get by with enough practice, much like Kirby to Falco, Snake to G&W, Ice Climbers on virtually any CP stage... Oh hell, let's face it, only MK is good enough to entirely avoid any CP shenanigans. -_- Even Snake is not devoid of slightly disadvantaged match-ups, including our dear ROB, and is terrible on both Rainbow Cruise and Jungle Japes.
Sorry, looks like I forgot what I was arguing about and started rambling.
I think my point was that MK is the only rational choice if winning is all that matters... and you actually think the months of catching up you have to do in order to raise your MK skill level beyond your current ROB (or other character) skill level, and start to compete with people who picked MK up earlier, is worth the time. At the least, everyone except MK and maybe Snake should be supported by secondary characters with a more favorable match-up against the main's disadvantages. ROB certainly deserves his place in the upper tier of characters, whining about how bad he is doesn't do anything.