On kamado, the deflector itself gets very hot and you get radiant heat from the deflector that makes the meat surface on bottom side see a higher temp. Try doing double indirect. On KJ it means a set of deflectors in lowest position and then a second set of deflectors on the lower grate position, typically using the X-ring. Food on top grate position. This gives a second air gap and second set of deflectors and results in much more even heat on the meat. You can also do this by putting deflector on lowest position, use a couple foil balls or another heat-resistant spacer arrayed in a triangle, and put a pizza stone on top of the balls. Again to get an air gap and then a second insulator. I'm unfamiliar with Primo deflector arrangement but I'm sure it's doable as well.
No experience with offset, but I can make some guesses and suggest some things to try. Is it reverse flow?
If so, the grill body under the cooking grate (the middle air deflector plate) is a hot surface and will radiate heat, just like the kamado deflector above. If you can, try suspending a drip pan under your cooking grate, not to do anything to drippings, but to block radiant heat off the grill body. Radiant heat is line of sight, so you don't want the meat to "see" the grill body underneath. I can make more educated guesses if you post some pics of all aspects of your offset.
If not, the air coming out of the firebox is definitely going to cook the meat more on the direct impact side. I'd try using foil to make a "sail" or wind deflector, wider than the meat, and have it protrude down from the leading edge of the meat under the grate some inches, so you aren't getting the hot airflow constantly across the bottom surface of the meat. (Sorta similar to when people gently tent the leading edge of the meat with foil in an offset; you're trying to block the direct airflow sweeping across the bottom). Also, again, radiant heat off the fire itself - is your firebox positioned where the fire can "see" the underside of meat? Block that line of sight with something.