Mr Okusanya said the FCA was probably unable to force platforms to solve the litany of problems that have afflicted clients in any more timely a manner than has been the case.
But he thought many of the firms in question had been complacent about the task that faced them, and so should face a "commensurate" punishment.
Advisers have been blighted by a litany of problems since Aviva and Aegon commenced their replatforming earlier this year.
Issues included processing adviser charges, switching funds, processing income drawdown, facilitating Isa contributions, and others, as has been extensively reported by FTAdviser.
In May some advisers were calling on the regulator to intervene after months of disruptions on the Aviva platform showed no signs of abating but the FCA would not comment on specific cases at the time.
Then in July it emerged the Royal London owned Ascentric platform also faced problems following a technology upgrade.
Mr Okusanya said: "Given the damage done to the reputations of firms such as Aegon and Aviva I think if they had a way of remedying the problems they would have done it by now, so I am not sure what powers the FCA have that would help with that."
He added: "Every firm that has done a replatforming said they would learn from the mistakes made by others, but every one of them has messed up. I think the FCA should fine firms and it would make others think twice about replatforming and making the same mistakes. When something goes as horribly wrong as this has, there must be a punishment."
Both Aviva and Aegon have confirmed they have been in regular contact with the FCA.
A representative of Aegon said: "Aegon treats regulatory compliance seriously and we have kept the FCA fully updated, both in the lead up to integration and afterwards."
Despite repeated requests the FCA declined to comment on the issues faced by platforms, or whether any regulatory rules, such as treating customers fairly, were in danger of being breached by the debacle.
Mr Okusanya said many clients had suffered emotionally as a result of the problems, while some clients suffered financially.
This included many clients of the Aegon platform not receiving the income they were due for a period of twelve days.
But Aegon and Aviva have both pledged they would compensate clients who lost money during the replatforming.
Minesh Patel, an adviser at EA Solutions in London, said he has stopped placing new clients on the Aviva platform.
He said: "Aviva was the fastest growing platform of the ones we use, in terms of putting new clients on there. But now we will only use it for existing clients, and as far as we are concerned both Aviva and Aegon are out of the game."
A representative of Aviva said: "Many of the issues that customers and advisers have been experiencing since platform migration in January have now been resolved.
"Certain issues remain, and we have a detailed plan of releases scheduled to resolve these."
Mr Patel said he has seen little improvement in the service received since the platform technology was upgraded in January 2018.
He said he still had to wait up to half an hour on the phone to remedy a problem around the issue of putting new money into existing client accounts.
But, unlike Mr Okusanya, he said he doesn’t feel the issues he is dealing with justify an intervention from the regulator.
He said: "They are inconvenient for the adviser but I’m not sure that it justifies action from the regulator except in instances where the customer has been shown to have suffered financially."
Ian Lowes, managing director at Lowes Financial Management in Newcastle, also said the problems he experienced with the Aegon platform were continuing and the costs to his firm "continue to snowball".
But he questioned whether the regulator could take action even if it wanted to. He said: "I have no doubt everyone is doing all they can in what must be extremely difficult circumstances – and I believe that Aegon will ultimately be offering some sort of compensation for disadvantaged clients and advisers.
"I’m not sure what the regulator could possibly do other than slap some wrists further down the line."
david.thorpe@ft.com
