I've argued before that he was just that on the Grizzlies.  I'll still argue that he was more important to them than Conley.  He was the leader on a team that upset the team with the best record in basketball.
Being a top 2-3 wing defender in the league is a very solid asset, and every championship team needs a defensive stopper.  I think he could absolutely win a ring as the 3rd best player behind two scorers on a well-rounded team that likes to run.
I don't value TA that highly (top three player on a contender) but you clearly rate him at that level of talent. Fair enough.
For me, I think TA can be that Bruce Bowen type player. A key glue guy, a fourth or fifth best player on a contender. 
My view of the Grizzlies:
- Grizzlies core = Z-Bo, M.Gasol and Rudy Gay
 
- Top role players = Battier, TA and Conley in that order but with comparable overall value (little separation between the three).
- Then the rest of the supporting cast.
I didn't think Memphis was a contender without Gay but I do think they are a contender with him in the lineup.
Well I'm not talking about a 3 man team like Bosh on Miami, I mean on a really deep well-rounded team, like say the Mavs.  Replace Marion with TA and they're still a championship team.
Again, like I said he's far from an ideal 3rd guy so I really don't value him that highly, but I don't value Harden that highly either.  Are you thinking about him if he reaches his potential?  Because that's a different a story.  At this point in time I don't think any team would be happy with Harden as their 3rd best player.
Out of the West, who did you consider a better contender than Memphis, without Gay?  I had them in the top 3 behind Dallas and OKC.