Refer to page 6 of the AR7200BX manual. "2. Be sure all trims/sub-trims are disabled (zeroed) and all servo travel values
In the Parameters Menu, you have "B Control Behavior" set to "Transmitter".Disconnect any two of the motor wires before doing any bench setup work.
By SPORT FLYING I assume you mean flying circuits, an occasional loop, roll, and stall turn.
When doing your setup with the AR7200BX you need a pitch curve that will allow full travel. I do this with the Throttle Hold Curve since you are not going to be doing auto-rotations with this heli. I have mine set at 0, 25, 50, 75, 100. Throttle hold on the Throttle Curve is set to 10% just as on page 5 of the Blade 450X Instruction Manual.
So when doing your initial setup, you check for your max and min pitch in the throttle hold position which should be +12 deg, and -12 deg. Check Swashplate leveling step G, Cyclic Geometry J, Collective Range Step K, and Cyclic Limit L, all done in throttle hold.
For sport flying, I would set my STUNT throttle curve to something like 30, 30, 50, 75, 100. This would provide an idle-up for better control during landings and enable loops and rolls (but no inverted flying). You will need to experiment to get the power the way you like it on the low end. On the pitch, you have to go no lower than - 4 degrees. Use your STUNT pitch curve to set that, not the end point adjustments.
Next I would set my NORMAL Dual Rates to 80% on Aileron, Elevator, and Rudder, with 20% EXPO on those as well. My STUNT DUAL Rates would also be set to 80% with EXPO still at 20%. This will soften the control feel for you and yet provide more than enough control for sport flying.
When ready to test this out, you reconnect the motor wires, use a fresh battery, set transmitter to NORMAL Mode, Throttle Hold, Throttle low, connect battery, wait for initialization, set on ground. Throttle Hold Off, spool it up to just below 1/2 throttle. Then switch to STUNT mode and lift off and fly around a little. When you bring her in, reduce the throttle and see how stable the descent is back to a hover. If the rotor appears to be too slow for good control, you need more rotor speed for the descent. Increase your STUNT throttle curve at the low end to bring the speed up a little.
That should provide you with a nice flying SPORT machine. When ready to fly 3D all you need to do is change your STUNT Throttle and Pitch Curves. Or you might just copy what you have to a new memory location and create a new profile for 3D flying, keeping the sport profile in tact if you want to go back to it. It's your call. A more advanced transmitter such as the DX8, DX9 or DX18 would give you Normal, Stunt 1 and Stunt 2 modes which would enable you to switch back and forth between SPORT and 3D anytime with just a flip of the switch.
I am quite certain I have said enough here that others will jump in with their own opinions. I have only been flying a 450 for two years and have re-built it many times. I wish I had just stayed a SPORT FLYER.
"Sweet dreams and flying machines in pieces on the ground." J. Taylor