No, they don't. I know from experience.
If I lose while using Siegfried, I've lost and my opponent has won. My character didn't lose, their character didn't win, the match-up didn't beat me - I lost, they won. Nothing more, nothing less.
As to why I'm still playing Siegfried, though...I guess you could call it dumb character loyalty, or that I'm just stupidly stubborn. The romantic reason is that I've been playing Siegfried since I was 7, all the way back in Soul Blade, so there's a sense of history and nostalgia to go along with him. So it's more of a emotional reason than a logical reason for why I'm still playing him, but I'll continue to play him even if he ends up bottom tier in SCV (he won't.)
One good thing I can say on playing lower tiers - GENERALLY SPEAKING, you have to think outside the box a little bit more than with higher tiers. As Hates said, this doesn't apply to all high tiers at all, just some. However, when you get a high tier character who IS easy to use, you don't really have to think or do much outside of your EasyPunish
®, EasyC
ombo™, and EasyRingout
©. Generally speaking, the opposite is also true - some mid tiers don't have EasyPunish
®, and they have to think outside the box a bit more.
For example, Siegfried doesn't have any "good" lows, so I was forced to abuse the shit out of his grabs and mix them up with similar speed mids. Since this is Soulcalibur, and all throws (non-command) are the same speed, this is something that could theoretically carry over to any character (who doesn't have tiny ass T-rex arms - Sophitia and Voldo!) regardless of tier placing. So I could take this strategy I developed with Siegfried and use it with Mitsurgui, or Cervantes, or Ivy or Astaroth - the latter two obviously gaining the most benefit from this style, but the point being is that I can use it with just about anyone who has a normal or longer grab range.
Another Siegfried player post, another wall of text...