... it seems to me that the Orange-SLS is not powerful enough to put Orion+EUS in LEO
This was already a topic a little earlier. The EUS is indeed quite heavy and needs a different ascent profile:
Because of the higher mass of the EUS the inital acceleration is slower. So wait a little longer before tipping over after launch, and aim for a higher orbit, like 300 km.
Just before burnout of the first stage pull up to +30° to build up positve vertical speed (+1000 m/s). This will help to gain speed with the EUS, rather than fighting gravity with this stage when fully fueled.
Have the Surface MFD open and watch for the vertical speed. If it approaches 0, pull the EUS up +30 or +40°, to keep the vertical acceleration around zero.
The Block 1B SLS could indeed stand more powerfull boosters to ease ascent, but I am not sure if this planned.
For an autopilot you could give the Launch MFD a try (but I don't know if it works for multistage launchers).