I should qualify that I do not think, nor did I say, that the idea of a five man attack is absurd. Quite the contrary in fact; I think it's very important to have a competent fifth bowler unless your four man bowling attack is both well balanced and vastly superior to the opposition's batting lineup. You may have noticed that I selected Miller to bat six in the Australian All-Time thread, which backs this up. What I do think is absurd is making a player who thrived in (and arguably largely because of) the number seven role at Test level bat six at a much higher level in pursuit of a better fifth bowler. Sobers may not be good enough to be a specialist bowler at this hypothetical level of cricket, but a genuine bowler he was, and as the fifth member of a five man attack I'm sure his bowling would be competent. The team already has a five man bowling attack, so playing so many bowlers doesn't even add to the depth of the attack as such;, it just raises the quality of a bowler who will probably only bowl about 10-15% of the team's over at the expense of a much needed specialist batsman and probably at the expense of Gilchrist's effectiveness too.
The Flintoff example is different for many reasons. Firstly, Flintoff during that period was holding his place as a batsman anyway - between the start of 2003 and the end of 2005 he had scored over 2000 runs at an average over 40 with four hundreds; this was as good or better than what you could expect from the next unproven county batsman in line. Comparing it to our situation here, do we think Imran could average 40 playing against what we can only assume will be bowlers of a roughly equivalent standard to Earth's all-time team? Do we think he'd do roughly as well as Headley, Tendulkar, Richards or whoever else got left out so five bowlers could play? Unlike the situation with Flintoff at the time, there are far better top seven batting options to choose from. Furthermore, England needed that fifth bowler to ensure a good, well-balanced attack a lot more than the all-time Earth team does; Giles had to play to ensure balance and variety in their bowling attack with a genuine spin option, but he was too poor a bowler to be relied upon as part of a four man attack. To add to this, England did not have a 'replacement' fifth bowler anywhere as good as Sobers, even relative to standard, had they decided to play an extra batsman and move Flintoff to seven or eight.