But didn't at least one of the defence experts argue the wounds were consistent with an 'escalating' sexual attack? The prosecution saw the lack of obvious defence wounds and jumped to the conclusion that meant multiple attackers, but as London John says, that would be just as consistent with an attack that progressed gradually, in which the knife was used to force Meredith to comply rather than to seriously wound (initially). Obviously if someone holds a knife to your throat, fighting back isn't always the best option regardless of how many years of karate you've done (well, I would assume that's obvious but given the assumptions by the prosecution, who knows...!).
The attack could've gone on for quite a long time before the serious wounds were made, with the major blood stain patterns and so on only being made at the end. I tend to think this sort of escalating attack is more likely for a few reasons: first because it fits the timescale better, if we assume that Rudy was already in the house when Meredith got back. I think the series of phone calls starting at 9.58pm marked the end of the attack, probably Rudy trying to switch off the phone. That would mean the entire attack, from start to finish until Meredith died, lasted a bit less than an hour - reasonable for an attack which escalated and became more serious as it went along, but quite a long time for a deliberate sexual attack which happened quickly.
And second, an attack which progressed gradually would seem to me to fit better with an assault that wasn't pre-planned by Rudy. What you describe seems more like a deliberate assault, not one that initially started with, let's say, a struggle (perhaps Meredith tried to scream, and he rushed over to silence her) and then progressed to something else. Although having said that, I suppose once the attack started the decision (if we can call it anything as measured as that) to assault her may have been made quickly. Either scenario seems possible (a very quick attack where she didn't have time to fight back, or an escalating attack which progressed more slowly) but to me the second option fits a bit better. At any rate, I certainly don't think there's anything to rule out a single attacker, and it seems like the police/prosecution made far too many early assumptions in deciding there must've been multiple attackers.