but surely they wouldnt be able to bowl 25 overs in a row. at least say you must use minimum 4 bowlers.
Do you not see the tactical balance that having to use at least five bowlers gives? If England only had to use four bowlers they could just play six batsmen, keeper plus say Broad, Swann, Bresnan and Anderson.
What the five bowler requirement does is means sides have several options, play an all-rounder who can bat and bowl, play a batsman who can bowl and hope they score enough runs that any lack of bowling is compensated in batting, or play five bowlers and hope they have enough batting.
It adds to the game, what makes it eminently different to Test cricket. What you're proposing is nothing short of, well short Test cricket.
And while two pace bowlers might not be able to bowl through, I'm guessing in a lot of games Sri Lanka might have had Murali on one end throughout. If a side has one or two good bowlers it works in their favour with no bowling allocations.
The real test, and what makes ODIs arguably the best format, is that sides with the strongest links in the batting order and no weak links in their bowling will be the best. England had the best side in 1992, didn't quite work out for them but they were strong throughout the side. You change the bowler allocations, and it will never happen anyway, and you aren't really playing an ODI at all.
Even worthless-duck method ruins a game by moving the goalposts, if one bowler had a stonking game he could decide a game in his 10 overs, but if rain means the side bowling second might have won had they bowled their 50 overs, but because that bowler can only bowl say five then the opposition get away with it.
And what if Finn say takes four wickets, he's just finishing his second spell of three overs and then the rules have been changed so he can just carry on bowling. In the sensible allocations era the batting side can see him off and look to attack the weak fourth and fifth bowlers, in your suggestion they'd simply be bowled at by the two most effective bowlers and the tactical elements are gone.