I have paid back more than 28%, but that is the creditor's cut AFTER fees. My contributions equal over 50% of the original debt.
Yes, I have done well out of it, as you point out.
But....If i'd reclaimed all my charges before the IVA (or never been charged them in the first place!), my original debt would have been say 20% lower, so I would have had to have paid 28% of a lower amount to get myself debt-free. I reckon that would have saved me around £5K on what i have paid back.
As for being discharged from my IVA early, that doesn't happen. They run for 5 years unless you come to a full and final arrangement (or they fail)
Thankfully i have generous parents who lent me £11K to get it all finished with!