The Liam Williams would join Saracens for £170k less than his worth at the pinnacle of his career argument might work if the Scarlets played in London and Saracens played in Llanelli. But as they don't, the cost of living ridicules that argument.
The Regulations are jumbled on players leaving due to injury when they haven't been out for a year but the simplicity of it has been misguided.
Under Schedule 1, section 2, paragraph L it says that the following is not considered towards the cap:
(l) any Salary (other than payments or benefits caught by paragraph 1(q) of Schedule (1) paid during a Salary Cap Year to a Player who, due to injury, has not played or been a replacement for the Club during that Salary Cap Year in the Gallagher Premiership, European Challenge Cup, European Champions Cup, Premiership Rugby Cup or in more than 3 matches in any other Competition, on condition that:
(i) the application made by the Club must include an Injury Certificate certifying that the Player’s limited participation has been caused by injury together with all other requested documentation as deemed relevant by the Salary Cap Manager in order to consider the application fully and fairly; and
(ii) the Club has not brought in a replacement player under the injury dispensation provisions set out in Regulation 5.
For the purposes of this Regulation, a sevens tournament shall count as one
Competition match;
Paragraph 1(q) says:
(q) any payment or benefit in kind paid in respect of a Player in connection with his redundancy or the termination of his playing contract with the Club including all redundancy or termination payments or benefits in kind (whether paid or payable provided or to be provided voluntarily, contractually, pursuant to statute or otherwise). Any such payment or benefit in kind shall count as Salary in the Salary Cap Year in which the player contract terminates, irrespective of whether it is paid, payable, provided, or to be provided before, during or after the Salary Cap Year concerned;
Therefore whilst what has been paid up to now wouldn't count, their redundancy payments do count.
An injured player is defined as:
Player" means any Senior Player of a Club who sustains an injury which has prevented or is anticipated to prevent him playing rugby
(a) for a minimum continuous period of twelve weeks within a Season; or
(b) where the same injury spans two Salary Cap Years the injury is for a minimum of eight weeks within the Season of the Salary Cap Year in relation to which the injury dispensation is being sought, subject in each case to the requirement that once an injured player is selected in a match squad in any Competition fixture he will cease being an injured player;
Rhodes last played at the Premiership Final, but I can't find anything that says when he picked up his injury.
Figallo has been out with concussion since the Argentina v England match on 5th October, so he too has been out for 12+ weeks.
William's injury was announced on 25th October 2019, so he only reaches the 12 weeks on Friday 16th January.
There's a standard release clause that says a club can release a player without payment after 24 weeks. Provided Rhodes was injured earlier than 24th July, he would qualify.