I'd say there were only three genuinely poor attacks, in unchallenging conditions, Flintoff faced between 2001/02 and 2006/07 myself. New Zealand in 2001/02, New Zealand in 2004, and West Indies in 2004.
India in 2001/02 was decent enough.
Sri Lanka in 2002 had Murali if no-one else.
India in 2002 weren't the best but he still managed to fail.
South Africa in 2003 were pretty good.
Sri Lanka in 2003/04 had Murali and that alone was enough of a Test, and Vaas bowled pretty well most of that series too.
West Indies in 2004 was actually reasonably challenging in the first three Tests because the pitches had a bit in them.
South Africa in 2004/05 were pretty good.
Australia in 2005 were pretty good even though there were times when it was a one-man Warne.
Pakistan in 2005/06 were pretty good.
India in 2005/06 were pretty good and the pitches in the last two Tests offered a bit to the bowlers.
Sri Lanka in 2006 had Murali, and again that's enough.
He didn't play against Pakistan in 2006, but with their third-string they were rubbish FTR.
Australia in 2006/07 were pretty damn good.
There's 11 series in there - Flintoff batted well in 3 of them. This isn't good enough for my money.
Firstly, your idea of what constitutes a good bowling attack is biased and based around his failures. For example, the Indian bowling attack from 2002 was an absolute joke. Kumble and Harbhajan bowled poorly as they almost always do away from home and Zaheer, Nehra and Agarkar at the time are better left without mentioning a word. Certainly that attack posed less of a threat and certainly did not come anywhere near close to the quality of bowling that was often on display by Collins, Collymore and occasionally Fidel Edwards from 2004. Nonetheless, it is irrelevant, because the fact of the matter is that Flintoff's batting only came off age in the summer of 2003 on his next return to the side in the series against Australia.
In the period from the summer of 2003 to 2007:
-scored against SA, as good a bowling attack going around at the time after Australia
failed in SL, due solely to his inability to play spin.
-failed against the WI against a not so good attack
-scored against NZ against arguably the worst attack of the lot
-scored against WI against what was actually a pretty decent attack, or at least an attack that performed above expectations
-failed against SA against a good attack
-scored against a good Australian attack
-failed against a good pakistan attack
-scored against a good attack in India
-failed against an ordinary SL attack. Although to be fair he only had 3 innings.
-failed in the Ashes
In a period of 10 test series, he succeeded against 5 attacks, 4 of which were perfectly acceptable to great. This is no worse than a lot of regular test batsmen going around these days.
For example, lets take a look at Graeme Smiths record:
Failed against Australia
Failed against SL
Scored against a piss-poor Pakistan attack
scored against a poor England attack
failed against a good pakistan attack
scored against a poor WI attack
scored against a poor Kiwi attack
scored against a good SL attack
did ok against a good India attack
failed against a good England attack
scored against a poor Wi attack
failed * 2 against Australia
did ok against a poor NZ attack
failed against a good pakistan attack
did ok against a good India attack
scored against a poor pakistan attack(at least on those pitches)
failed against a decent NZ attack
scored against a good India attack
Thats 4 good series out of 12 and not much better than Flintoff Im afraid. Yet you happen to champion this man.