You shouldn’t be having any issues with Ultegras. They’re superb brakes, any more powerful and you’ll simply lock up all the time.
They’re a road racing brake and do a great job.
Check to see if the caliper moves the millisecond you pull the lever.
Avoid silly short runs.
Don’t ever use plastic outer cable ferrules.
Clean you rims.
Balance the stirrup.
Don’t over tighten the caliper to the frame. Torque correctly or else you’ll squash the mechanicals together.
What rims are you using and what state are they in before you try new pads. Some rims have dreadful braking surfaces.