Being placed in Support Group for re-instated ESA claim once UC has been claimed but no ESA WCA has been carried out

In March 2017 client was deemed not to have ltd. capability for work because of failure to attend WCA without good reason and hence irESA claim closed.
In June 2021 FtT issued a 24-page decision stating that he did have good reason!
Needless to say in the interim client was ‘starved’ into submission and reluctantly agreed to claim UC in 2019 and was eventually place in the LCWRA – no surprise given his severe physical and mental health issues.
4 months on from FtT DWP has finally agreed to re-instate irESA claim for the missing period at the basic rate which he was on at the time of the 2017 decision.
I had a conversation with the DM yesterday and tried to argue that he had the option to place my client in the support-group (as he would have been years ago had everything been done correctly) but he would not budge despite acknowledging that he was sympathetic to my point of view and that my client has lost out financially.
DWP had difficulty supplying the FtT with any contemporary documents (because of its bizarre GDPR policy of deleting everything 14 months after a claim is closed) but there is a LT54 which notes that:
 June 2015 Request from support worker for home assessment
 July 2015 – client submitted BF223 stating he was unable to attend ..due to being bed-bound
 Aug and Nov 2016 decisions allowing failures to attend on the basis of domestic visit (DV) requests and DM request that a home visit be made when allowing the Nov 2016 failure to attend.
Maximus does not seem to have acted upon this request/instruction for the DV so in 2017, when client again did not attend a WCA, DM does not seem to have followed up previous request DV ‘request’ and made the fatal ‘failure to attend without good reason’ decision.
At the time of the March 2017 decision ESA had a copy of a Care Act Assessment which stated client was bed-bound and further evidence was supplied with the mandatory reconsideration request in May 2017, namely a comprehensive psychiatric report and letters from consultants indicating the nature and severity of physical ailment.
My arguments so far as to why DM could consider now ‘retrospectively(?) placing client in ESA Support Group are:
 Reg 36 (2) ESA Regs 2008 – current DM has more than sufficient evidence to make such a decision – but they to insisting they could only do that after an ESA WCA which he was suggesting is not going to happen;
 Previous DM had requested DV but Maximus failed to follow up and then next DM seems to have completely ignored this previous request and made failure to attend decision – all of which strikes me as bordering on maladministration – but current DM was not about to be guilt tripped into change their mind
 Retrospective placement in ESA support group once a person is claiming UC is envisaged by DWP as indicated in ADM para F5052 and accompanying examples although my client has never attended an ESA WCA;
 Reg 20 UC (Transitional Provisions) 2014 – note in ‘Sweet & Maxwell Vol.5 (admittedly my copy is from 2016/17 as my manager blanches when I ask for funding for up-to-date version!) again suggests the award of LCWRA for a closed ESA claim post a UC award can occur
 finally I suggested ‘reverse engineering’ entitlement to ESA support group as client is in has LCWRA for UC – but common sense did not prevail.
I am awaiting the written decision and am minded to submit a mandatory recon. So any suggestions would be welcome or should I just go straight for a compensation claim for the ‘lost’ ESA support group component?

Update on this case - DWP has finally agreed that claimant should have been deemed to have LCWRA from July 2015 and has subsequently paid 4 years worth arrears of this (up to the date claimant finally claimed UC)  , plus payment of a couple of more years worth of sdp and edp that it still owed.  A consolatory payment of a yet to be decided amount will also be paid and a couple of more months of HB should be awarded for good measure.