Online ranks don't mean anything so it doesn't matter. You're just as likely to beat or be bodied by a "Ruby" Rank or an F Rank. It doesn't matter how "high level" a player is online, it's impossible to play the game in a legitimate fashion online. Even in a "good" connection, the matches are still nowhere close to simulating an offline match. Don't underestimate how much even the slightest amount of lag fucks over DOA5U's gameplay. Movement gets screwed over big time for example and you can't react to stuff like you're supposed to. In short, online matches are never legitimate ever. Doesn't matter which two players are involved and thus doesn't mean anything if you're able to beat someone like SonicFox or Mr. Kwiggle online.
I admit that 5U's Level 8 AI can still be pretty ass, but it at least somewhat plays the game legitimately. It does tend to hold on reaction a fair bit, but from what I've seen it doesn't hold you any faster than someone like SweetRevenge or XcaliburBladeZ could hold you. The AI attempts to simulate how the game is played at a high level in Japan (in terms of fundamentals), although I wish the AI would use slightly more advanced tech and wouldn't keep falling for CB setups. If you were to play a "high" level player offline, they'd easily hold you just as much as the AI does. So IMHO, I'd rather fight the Level 8 AI then engage in a nonsensical laggy clusterfuck of a match online.
However, both situations pale in comparison to a legit offline match by a long shot.