The competent person you speak of is only there to assist in implementing the preventative/protective measures which really come about after the risk assessment is completed. Competent persons are required for other areas, i.e. evacuation, but none for the risk assessment.
As you say, regardless of this, guidance does indeed suggest the use of a competent person for complex premises or where the RP doesn't think they can do the risk assessment. So, if someone is told by an FRS that filling in some online form gives them a suitable risk assessment, then who are they to argue? Their own competency is not an issue, the suitabilty of the RA is the issue and are the local FRS (who almost 'promote' the method) going to find your RA unsuitable?
FWIW I also think it is wrong. We are a public service, we should not be allying with companies in this way.