I don't know about your finisher theory. I think a finisher is a special breed of batsman, and deserves his own place. I'd argue that you tried to make Sachin a finisher he wouldn't have the same success as a Bevan or a Dhoni. Some batsmen have a skillset more suited to the top of the order, while others are better at the role of a finisher. Doesn't necessarily mean that those at the top of the order are better.
Speaking of an all-time ODI XI, the selection depends on how much you value batters batting in their position. If you're just picking the seven best ODI batters in history (and I'd probably argue that Dhoni has the numbers to challenge for one of those seven spots, plus the intangibles - leadership, killer instinct, etc), you might omit a finisher. But if you respect batting positions, then the number 6/7 spot basically comes down to Bevan v Dhoni, and you can go on opinion from there.
For me, Gilchrist doesn't make it into the best ODI XI. I'd pick Sangakkara as a keeper batsman at four, and leave the finisher's spot at 6. Sehwag gets anywhere near the team only if the matches are played in the subcontinent, otherwise I'm picking Haynes or Saeed Anwar with Tendulkar (hell, even Ganguly will do better than Sehwag).
Agree with almost everything that you said. Playing Gilchrist anywhere besides the opening spot doesnt make any sense because Gilly played more than 90% of his matches in that position.
Also, I would add Klusener to Bevan vs Dhoni battle simply because he would be very handy as an extra bowler with his fast mediums. Although in pure finishing skills Bevan/dhoni would beat him.
Anyways. This series will be a massive test for MSD - he has a brand new team. He is the senior player now. And his last 2 overseas series were disasters. He will have to think smartly and proactively if India is to challenge SAF in the field at all.
IMO, Finishers are not a special breed, they are players with limited capabilities who cannot bat at the top and score consistently . That is why such players always back themselves up with an additional skill , bowling in case of Bevan and Keeping in case of Dhoni . Such players might not find a place in the team solely on their batting skills or their other additional skill .
Finishers rarely do the bulk of scoring and when they get such an opportunity (in case the top order fails) they do not succeed most of the times (Dhoni's recent innings of 65 against SA is a good example of this . India could not even reach 250 and there might be other instances of this kind) .
In ODI's your best batsmen will always bat at the top , by best I mean batsmen who can face almost anything thrown at them, score runs briskly, bat through the innings if possible and keep their wickets intact and do this consistently enough to justify their position at the top .
Their(Finishers) success is inextricably linked to success of top order . As a result you will find these finishers only in teams with strong batting line up .
If the batting line up is weak these finishers will not thrive because too high a demand will be placed on their batting skills as they will have to score significant portion of the runs scored by their team , that to very frequently which they cannot do (and if they start scoring runs constantly then they will be moved up the order and they are no longer finishers, they are proper batsman) So if Dhoni walks into a team having weak batting line up he might not do well . He has not shown the inclination to come up the order even in South Africa where he is the senior most ODI batsman of Indian team . That says a lot about his confidence in his own batting skills .
As for Sachin , if I am not wrong, for the first 90 odd odi's he played at 5,6 and 7 and for a 16 year old he did pretty OK . AFAIK, Sachin was eager to go up the order right from the beginning . Even as a kid he seemed to be confident about his batting skills though he had never opened an innings before in any form of cricket(school/domestic/international). All through these 90 matches he repeatedly requested to go higher up the order and once he got to the opening slot he made sure that he became the best ODI batsman that ever was . If he had stayed at 6 and 7 he would not have being considered good enough to be the greatest . He moved up because he had complete confidence(as a 16 year old) in his batting skills .
A good ODI batsman may start out as a finisher at 6, 7 or 8 but if he
chooses (which Dhoni has) to remain at 6 and 7 then it will always raise doubts about his ability as a batsman
This guy and
this guy , at their peak , are much better than Dhoni and more suitable at 6 or 7 .
The Only way Dhoni could have snuck into an ATG ODI team was as a wicket keeper . But here too , Gilchrisht and Sangkarra( somehow missed him in my initial post
) score over him .
So no Dhoni is not even close to been the greatest ever ODI batsman of either the world or India and I guess the ship has already sailed for him .
You got your answers through other's replies. The kind of impact that you have in a particular format determines where you are the best batsman in that format or not. Dhoni's impact for India in ODI's has been massive almost ever since he started playing for India. In fact, his value has grown exponentially high after he became captain. Before he was a dasher who could finish games quickly for India. Then he became this cool head who doesn't fear any situation in ODI's. To me, Dhoni can easily compete alongside Tendulkar for the greatest batsman for India in ODI's.
P.s: Ask anyone here and they'll say I am a huge Tendulkar fan (at times, fanatic). So if you think I have something against Tendulkar, rest in peace.
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Kohli has amassed most of his runs at home (barring a few innings here and there abroad, and that too in helpful batting conditions). Dhoni gets runs everywhere in ODI's. Currently on form, Kohli might be the best ODI bat, but in the current Indian team, there is a better ODI bat than Kohli.
I was not looking for any answers . I was expressing my opinion and answering a question raised by you .
As for Dhoni he is neither India's nor World's best ever ODI batsman and now it is too late for him . He can become India's most successful captain .
Please See that I have listed SRT and MSD as my favourite batsmen . 
What a knock..
This is how Indian bowlers pass through their career. They do well in domestic. BCCI pick them for national T20 side, then for ODI side then for Test side. Now then, that bowler becomes team crucial part, BCCI keep selecting them in all the 3 formats and he mostly of times gets selected for every match. Bowler don't get that much needed fitness. Now India gets a reserve bowler. 
