LO,
I was around on the programme when the gun was switched. The reason given for the switch was that Mauser had not managed to demonstrate a working linkless feed system for the cannon, as well as blast issues.
They switched to the 25mm Gatling, citing better effectiveness and easier integration. However, in my view the real reason for the switch was a very strong and effective lobby from US gun makers that exploited the US user community's long standing preference for Gatling designs. The analysis that was offered by the F-35 team that led the change did not mention the increased volume, increased weight, reduced duration of fire and quite significantly reduced effectiveness, especially in the air to ground scenario, of going to a 25mm Gatling. (The 27mm round is really very good indeed - the 25mm isn't bad, but the 27 beats it all ends up).
The main problem at the time was that LM had taken their eye of the weight ball - big time. They didn't think they had a big weight margin, they just weren't really thinking about weight (of any of the variants) at all. Big mistake for a combat aircraft.
I'd respectfully disagree about strafing - modern gunsights are damn good and getting better with a good EOTS to help aim them. Guns offer a very effective 'low collateral' weapon, in my view. If it really is 'too dangerous' for jets, well, perhaps we had better get a few more attack helicopters to fill the close support gap.
Best Regards as ever to those working the programme,
Engines