The confusion obviously over the term 'stock bowler'. 'Part time' or 'fill in' may be a better term.
As for the answer, I wouldnt worry about it. You only need 10 overs a day approx. They dont have to be good, they just need to offer something different like Richards, Border, Boycott etc have done to a certain extent.
4 bowlers are enough to get the job done. 20 overs a day isnt an issue. Less than 1 spell per session. 'Part timers' are there to fill in if a rest is needed, or the game is meandering or to try something different.
I wouldnt be too bothered about how good they are. Obviously the better they are the better it is, but you are not going to win games (obvious rare example excepted) with the fill-in bowlers.
Sehwag and Ganguly are just fine, as long as they are not expected to fulfil a front line responsibility.
EDIT- Interestingly, Im looking at a random scorecard and it happens to be a game that India went into with only 2 specialist bowlers. Amazing.
Man for man, Ganguly and Sehwag can perform well as stock bowlers. Match for match, however, they don't get a chance.
The 'part-timers' don't provide enough rest- either they are introduced very late, or they are taken off after a very short time. That's how an out-of-form RP Singh or an out-of-ammunition Kumble bowled all those overs. If Kumble is bowling over 35 overs in every innings, without getting much, there is something wrong, either with the bowler, or the pitch, or (worse) the fielding. At least 15 overs can be taken off him by Sehwag.
A full front-line responsibility isn't important- that they have to have three slips and a gully, or open the bowling, or even final overs. They just have to hold one end up for a long time, so that the main bowlers recharge and come back better- and their series or match figures end up better.
Look at most of the best Test teams around. They've got (at least) five bowling options, with the notable exception of Australia- and even they feel the pinch after the retirement of McGrath and Warne. New Zealand's bowlers, individually, are not much good, but with help from Styris and Oram, are an effective bowling unit. South Africa have had Kallis bowling long spells, and while returns from one man haven't been remarkable, the whole unit does well. And of course, who can forget Sanath's services for the Lankan team? Or Gayle? At least one Indian batsman should do that.