I was wandering about that... In any case, it only requires a minor change to the code (see below). In your OP you mentioned DelimitedSplit8K so I won't go into details about it or where to get it.
There are only 3, very simple,changes that need to be made...
#1 use a single CSV parameter rather than separate parameters.
#2 in the 1st CTE, split the SSV parameter with the help of DelimitedSplit8K.
#3 in the WHERE clause, use "LEN(@_mv_skill_param) - LEN(REPLACE(@_mv_skill_param, ',', '')) + 1" to determine the number of elements in the CSV
... super easy...

USE tempdb;
GO

IF OBJECT_ID('tempdb.dbo.Skill', 'U') IS NULL
BEGIN -- DROP TABLE tempdb.dbo.Skill;
  CREATE TABLE tempdb.dbo.Skill (
   skill_id INT NOT NULL IDENTITY(1,1),
   skill_name VARCHAR(30) NOT NULL
   CONSTRAINT pk_Skill PRIMARY KEY CLUSTERED (skill_id),
   CONSTRAINT uq_Skill_skillname UNIQUE (skill_name)
   );

  INSERT tempdb.dbo.Skill (skill_name) VALUES ('C#'), ('.net'), ('C++'), ('T-SQL'), ('PL SQL');
END;

IF OBJECT_ID('tempdb.dbo.Candidate', 'U') IS NULL
BEGIN -- DROP TABLE tempdb.dbo.Candidate;
  CREATE TABLE tempdb.dbo.Candidate (
   candidate_id INT NOT NULL IDENTITY(1,1),
   first_name VARCHAR(30) NOT NULL,
   last_name VARCHAR(30) NOT NULL,
   CONSTRAINT pk_Candidate PRIMARY KEY CLUSTERED (candidate_id)
   );

  INSERT tempdb.dbo.Candidate (first_name, last_name) VALUES
   ('Bob', 'Jones'), ('Mary', 'Baxter'), ('Kevin', 'Hall'), ('John', 'Doe'),
   ('Alison', 'Chains'), ('Molly', 'Hatchet'), ('Maxwell', 'House'), ('Red', 'Fox');
END;

IF OBJECT_ID('tempdb.dbo.CandidateSkills', 'U') IS NULL
BEGIN -- DROP TABLE tempdb.dbo.CandidateSkills;
  CREATE TABLE tempdb.dbo.CandidateSkills (
   candidate_id INT NOT NULL,
   skill_id INT NOT NULL,
   proficiency_level INT NOT NULL
    CONSTRAINT ck_CandidateSkills_proficiencylevel CHECK (proficiency_level BETWEEN 1 AND 5),
   CONSTRAINT pk_CandidateSkills PRIMARY KEY CLUSTERED (candidate_id, skill_id)
  );

  INSERT tempdb.dbo.CandidateSkills (candidate_id, skill_id, proficiency_level) VALUES
   (1, 1, 3), (1, 2, 2), (1, 5, 4), (2, 1, 4), (2, 3, 2), (2, 4, 1),
   (3, 4, 5), (3, 1, 1), (4, 5, 5), (5, 1, 2), (5, 2, 2), (5, 3, 3),
   (5, 4, 1), (5, 5, 2), (6, 2, 4), (6, 4, 4), (7, 1, 3), (7, 3, 3),
   (6, 5, 2), (7, 5, 5), (8, 1, 4), (8, 4, 4);
END;

--SELECT * FROM dbo.Candidate c;
--SELECT * FROM dbo.Skill s;
--SELECT * FROM dbo.CandidateSkills cs;

--=======================================================================================

DECLARE
  @_mv_skill_param VARCHAR(8000) = '1,3,4';    --<< using a single CSV parameter... compatible with SSRS MV parameter output.

WITH
  cte_required_skills AS (
   SELECT
         skill_id = ds.Item
        FROM
            dbo.DelimitedSplit8K(@_mv_skill_param, ',') ds
   ),
  cte_cs_eval AS (
   SELECT
    cs.candidate_id,
    cs.skill_id,
    cs.proficiency_level,
    skill_count = COUNT(1) OVER (PARTITION BY cs.candidate_id),
    total_proficiency = SUM(cs.proficiency_level) OVER (PARTITION BY cs.candidate_id)
   FROM
    cte_required_skills rs
    JOIN dbo.CandidateSkills cs
      ON rs.skill_id = cs.skill_id
   )
SELECT
  c.candidate_id,
  c.first_name,
  c.last_name,
  s.skill_name,
  ce.proficiency_level
FROM
  cte_cs_eval ce
  JOIN dbo.Candidate c
   ON ce.candidate_id = c.candidate_id
  JOIN dbo.Skill s
   ON ce.skill_id = s.skill_id
WHERE
  ce.skill_count = LEN(@_mv_skill_param) - LEN(REPLACE(@_mv_skill_param, ',', '')) + 1    --<< counts the delimiters and then adds 1
ORDER BY
  ce.total_proficiency DESC;

HTH,
Jason