You don't need people trying to fix it - you need people to find the problems.
A friend was telling me of his company's experiences being drafted in to help fix a major project after it went live
His boss had an excellent reputation for not panicking.
There was a big meeting - sorry a meeting with lots of decision makers making decisions.
The conversation went a bit like
Him: "what is the perceived problem and what evidence is there for the root cause"
DMs: It is slow - we are rewriting the programs
Him: What evidence do you have?
DMs; We are rewriting the problems.
Him:What makes you think it is the programs and not the database.
DMs: We have lot of coders.
Him: Can we get evidence on 1) database 2) CPU hot spots 3) locking... I'll send my team home until tomorrow morning
Him:It looks like evidence there is a database problem.
DMs: Great - we'll change the database
Him: Can we get evidence on where in the database it is slow. Is it slow disks, or a bad index?
DM: We'll change the programs to work round it.
Him:It looks like the indexes have been badly designed and we are missing some...
If you want to use your coders, they can fix the application logic and implement field validation.