For the sake of clarity and not perpetuating misunderstanding; that claim that Howard "reshot 70%" is something of a misnomer. It actually comes from
this article in Variety which claims: -
"When Howard came aboard, it was mandated that 85% of Lord and Miller’s “Solo” be reshot, including second unit material. Howard’s work ultimately comprises 70% of the finished film."
My understanding is that L&M were fired while they had done most of the location shooting & second unit, and just starting shooting on the soundstage. So it's not like the film was 100% complete and they reshot 70% of it, but more like the film was about 30-40% complete (footage-wise, not counting post production obviously), reshooting most of that AND finishing the parts of the movie they hadn't even gotten to yet. So in reality, the actual reshoots probably don't amount to much more than 20-30% of the final picture, and a good chuck of that is second unit.
That article also makes it clear that the real "creative differences" weren't about improvising on the script persee, but how much it was eating into the budget by going overtime. That doesn't sound like a fireable offence until you consider that going overtime means paying the crew overtime money, which could be double, or triple the usual rates depending on the kinds of hours and days of the week you're talking about. Pretty quickly you can find yourself having spent a whole month's budget in just a week, with only the footage that should have taken a day and a half to show for it. Plus of course the mess that makes of the schedule, since every delay pushes everything else down the line, which requires even more overtime, and more expenditure.
You can get away with that kind of thing on lower budget and/or indie movie. But on a production like this? Not without a damn good reason, and certainly not as often as they apparently tried to get away with. What this comes down to is directorial mismanagement. They just weren't ready for the scale and responsibility of a production like this, and were very poorly prepared. Kennedy did her job as a producer and removed them before the whole thing imploded, then hired someone that actually knew what he was doing.
This isn't even the first time something like this has happened in a Star Wars movie. There's a very good reason why Irvin Kershner and Gary Kurtz did not come back for RotJ. tESB went way over budget, largely because Kersh was somewhat of a perfectionist on set (a less flattering way to put it would be "fussy") and that similarly led to a lot of overtime. It was Kurtz's job to manage that and reign him in, which he kinda didn't. Hence; Lucas didn't ask them back, and very deliberately hired a Director more used to working in TV and thus well accustomed to marching to the EP's tune instead of his own, and more crucially; being economical with the crew's time.
Let's also be clear on one thing: disappointment or not (a useless metric anyway given it's subjective and arbitrary nature) Howard and Kennedy managed to deliver 'Solo' as a profitable movie, by a good $100M margin. Had the ripcord not been pulled when it was, then it really would have been a disaster.
