There is actually a community of ~20000 people using some forms of this: codeforces.com. The most used approach are lots of macros in C++ to completely modify the language. One popular alternative is https://cpeditor.org/.

For example, look at how Benjamin Qi does it: https://codeforces.com/contest/1446/submission/98447974

The actual code is at the bottom. Here is a sample of a submission to a problem harder than your usual AoC second part:

  int main() {
   setIO(); re(N,M);
   str A,B; re(A,B);
   F0R(i,N+2) F0R(j,M+2) mx[i][j] = -MOD;
   int ans = 0;
   R0F(i,N) R0F(j,M) {
    ckmax(mx[i][j],mx[i+1][j]);
    ckmax(mx[i][j],mx[i][j+1]);
    if (A[i] == B[j]) {
     dp[i][j] = 2;
     ckmax(dp[i][j],mx[i+1][j+1]+4+i+j);
     ckmax(mx[i][j],dp[i][j]-i-j);
     ckmax(ans,dp[i][j]);
    }
   }
   ps(ans);
  }