Ehm, Kirge in fact
WAS a SternRitter ... Opie "J" the Jailer. And he was keeping shikai Ichigo busy, bankai Ichigo overpowered him quite quickly. Opie himself stated that. It was just because Opie was a lot smarter than the SternRitters Kenpachi's beaten that he lasted that long. From what we saw and heard we can almost even say that the SR that fought Kenpachi never used Vollstandig or Sklaverei.
Kenpachi won just because of his brute and raw strength and that he has 'no nonsense' attitude. Ichigo was trying to get some information from Kirge.
Apart from that I agree that the match between Ichigo and Kenpachi in SS arc was for plot. It ended in a draw. (It's funny because Ichigo thought he lost and Kenpachi thought that he lost instead.)
And I think there is a good explanation to why it ended like that.
As it was stated, Kenpachi's "ability" is probably that he matches the strength of his opponent when he's enjoying his fight. That's why he he fought to a draw with Ichigo, because he was having fun.
He won with Tousen, because it was boring.
He was in a draw with Noitra when it was still fun but when it got boring he overpowered him.
He lost the last match with fake Juha Bach because he probably didn't have time to match the fake's strength...or for some unknown reason.
This whole debate doesn't even matter.
The entire fight was nothing but plot progression for Ichigo. Let that be the end of it.
Let me try to close this once and for all:
-Kirge was just a Vandenreich Lieutenant. He wasn't even a Stern Ritter, yet he managed to keep Bankai Ichigo busy for a hefty amount of time.
-Kenpachi killed 3 full-fledged Stern Ritters without breaking a sweat.
Now, Shikai Ichigo > Kenpachi? DON'T MAKE ME LAUGH.
This whole Shikai Ichigo vs Kenpachi garbage needs to stop.