혹시 원하시는게 이런게 아닐런지요?
빨간부분만 소트해서 될게 아니란 생각이 듭니다.
전체적으로 레벨별 소트를 해야 하지 않을까요?

WITH t AS
(
SELECT 'srvc01' srvc_id, 2 sort_key FROM dual
UNION ALL SELECT 'srvc0101'  , 2 FROM dual
UNION ALL SELECT 'srvc010101', 3 FROM dual
UNION ALL SELECT 'srvc010102', 2 FROM dual
UNION ALL SELECT 'srvc010103', 1 FROM dual
UNION ALL SELECT 'srvc0102'  , 1 FROM dual
UNION ALL SELECT 'srvc02'    , 1 FROM dual
UNION ALL SELECT 'srvc0201'  , 2 FROM dual
UNION ALL SELECT 'srvc020101', 2 FROM dual
UNION ALL SELECT 'srvc020102', 1 FROM dual
UNION ALL SELECT 'srvc0202'  , 1 FROM dual
)
SELECT LEVEL lv
     , srvc_id
     , sort_key
  FROM t
 START WITH LENGTH(srvc_id) = 6
 CONNECT BY srvc_id LIKE PRIOR srvc_id || '__'
 ORDER SIBLINGS BY sort_key
;

ORDER SIBLINGS BY srvc_id, sort_key

원하시는 결과가 최초 설명하신게 맞다면?
같은 레벨 연속인 경우에만 순서를 조정한다면
그러나, 다음과 같은 예시자료를 만난다면 데이터가 이상하게 꼬이게 됩니다.
즉, 2레벨의 순서가 조정되면서 3레벨은 2레벨을 쫒아가야 하는데 그게 안되죠.

WITH t AS
(
SELECT 'srvc01' srvc_id, 2 sort_key FROM dual
UNION ALL SELECT 'srvc0101'  , 2 FROM dual
UNION ALL SELECT 'srvc0102'  , 1 FROM dual
UNION ALL SELECT 'srvc010201', 3 FROM dual
UNION ALL SELECT 'srvc010202', 2 FROM dual
UNION ALL SELECT 'srvc010203', 1 FROM dual
)
SELECT srvc_id
     , sort_key
  FROM (SELECT srvc_id
             , sort_key
             , DECODE(LENGTH(srvc_id)
             , LAG(LENGTH(srvc_id)) OVER(ORDER BY srvc_id)
             , 0, 1) flag
          FROM t
         ORDER BY srvc_id
        )
 ORDER BY SUM(flag) OVER(ORDER BY srvc_id)
        , sort_key
;