The west this year is too strong, I just can't buy your argument. Check the wagesofwins formulas. Manu's been worth like what 10, 12 wins already by himself? Plus it's really not very realistic to expect a team of 35 year olds to play every regular season game in a grueling 82 game season like their hair is on fire. Their bodies just cannot handle it. With the Spurs the issue isn't motivation as much as it's just pacing. They have to pace themselves to get to April and May and hopefully June.
Really your whole hypothetical argument just doesn't make much sense. You can't just up and pretend the roster has no les and lots of motivation to play super hard. No NBA roster would be built like this unless they specifically did have championship experience and lots of experience playing together. Pop's whole excuse for bringing the whole team back this year was that they deserve a chance to repeat together. If they didn't win in '07, than Horry, Bowen, Barry, Fin, Vaughn etc. would all be gone already.
I think you are not giving enough credit to the teammates that both Tim and Manu had around them from 1989-2002. Not always championship caliber teams, sure, but plenty of talented players and contending squads. Elliott was a fine player in his prime and so was mings. Strickland had a good run for a while and so did Avery. And at least in half those years the East was the superior conference to the West, so the compe ion wasn't as hard.
As for the Duncan era, don't let your memories of the '03 Robinson cloud the total package. For most of the time he played with Timmy, David was still a good player, an asset, and definitely superior to the cast of jokers, castoffs, misfits and ne'erdowells we've had at center since.
And also, please remember that the '08 Duncan is not in his prime. He can't carry a club like he used to.