We are left with following problem, upon which TcT provides the
certificate YES(?,O(n^1)).

Strict Trs:
  { revApp#2(Nil(), x16) -> x16
  , revApp#2(Cons(x6, x4), x2) -> revApp#2(x4, Cons(x6, x2))
  , dfsAcc#3(Leaf(x8), x16) -> Cons(x8, x16)
  , dfsAcc#3(Node(x6, x4), x2) -> dfsAcc#3(x4, dfsAcc#3(x6, x2))
  , main(x1) -> revApp#2(dfsAcc#3(x1, Nil()), Nil()) }
Obligation:
  innermost runtime complexity
Answer:
  YES(?,O(n^1))

The problem is match-bounded by 2. The enriched problem is
compatible with the following automaton.
{ revApp#2_0(2, 2) -> 1
, revApp#2_1(2, 3) -> 1
, revApp#2_1(5, 4) -> 1
, revApp#2_2(2, 6) -> 1
, revApp#2_2(5, 6) -> 1
, Nil_0() -> 1
, Nil_0() -> 2
, Nil_1() -> 1
, Nil_1() -> 3
, Nil_1() -> 5
, Cons_0(2, 2) -> 1
, Cons_0(2, 2) -> 2
, Cons_1(2, 2) -> 1
, Cons_1(2, 2) -> 2
, Cons_1(2, 2) -> 3
, Cons_1(2, 2) -> 4
, Cons_1(2, 3) -> 1
, Cons_1(2, 3) -> 3
, Cons_1(2, 4) -> 1
, Cons_1(2, 4) -> 4
, Cons_1(2, 5) -> 1
, Cons_1(2, 5) -> 2
, Cons_1(2, 6) -> 1
, Cons_1(2, 6) -> 3
, Cons_2(2, 3) -> 1
, Cons_2(2, 3) -> 6
, Cons_2(2, 6) -> 1
, Cons_2(2, 6) -> 6
, dfsAcc#3_0(2, 2) -> 1
, dfsAcc#3_1(2, 2) -> 1
, dfsAcc#3_1(2, 2) -> 2
, dfsAcc#3_1(2, 2) -> 4
, dfsAcc#3_1(2, 4) -> 1
, dfsAcc#3_1(2, 4) -> 4
, dfsAcc#3_1(2, 5) -> 1
, dfsAcc#3_1(2, 5) -> 2
, Leaf_0(2) -> 1
, Leaf_0(2) -> 2
, Node_0(2, 2) -> 1
, Node_0(2, 2) -> 2
, main_0(2) -> 1 }

Hurray, we answered YES(?,O(n^1))