Grind offline until you’re able to compete man. Lots of career arcs that can get you a good team.
When it comes to online play, Diamond Dynasty and similar modes only truly work if you feel compelled to get the best players to be able to compete online at the highest levels. If you can compete with anyone by having Joey Gallo and Kyle Schwarber on your team, then the mode isn’t working. The fact that you are complaining about this proves the patch is creating that need to collect better players.
But at any rate, there are online modes, such as Events and BR, which put restrictions on the players you can use and help level the playing field. Maybe you should play those until your team gets better.