Super Mega Baseball 3

Create a custom team and edit each players' stats to 99 in each category.

Start a Custom Franchise and Create a new Custom League. Conferences and Divisions off, 4 teams, Add Team Method 4. Scroll down to the teams and swap one of the 4 teams for your super-powered custom team (select change team and hit X to swap over to 'Gamertag's Teams'). Swap one of the other teams to the Nemesis (since they already have a couple of A+ rated players, the rank below S)

You should now have a 4 team league with your Super Powered team, the Nemesis, and two other random Super Mega League teams.

Start a new Franchise with this custom league and choose the Nemesis as your player-controlled team

Games per season 16, 1 Inning, 1 Playoff Game, 2 Playoff Teams.

Since the super-powered team in your league has such a high payroll, your normal Super Mega League standard team should now have way more payroll surplus than you'll ever need (check in the Economy tab)

Now you can just Sim a game, buy all the Player Development upgrades, sim game, buy the PDOs, repeat until one of your players flips to S rank. Shouldn't take too long unless you get really crummy luck with which PDOs you get. Since you're buying all of them every game, they'll refresh pretty quickly. If it does take more than one season, just make sure that you retain all of your A+ ranked players in the offseason.