Just to clarify, and yes I am an HVAC Tech.....What exactly did this guy tell you was wrong? If the compressor is bad, is it bad because of an additional leak or if he saying the physical compressor is leaking.
Also, You can use an A coil that has an R22 Base to it in a 410 System if the TXV is added or changed AND the coil is large enough for the capacity of the 410. Now, I agree its better to swap it all out and have a nicely matched system as they will be designed to work better together. And yes what you describe about colling air and not pulling humidity is true, a well Matched system to a house will cycle on warm days and may run nearly nonstop if we get to 90+ degress and this is normal and desirable.
If you have any other specific questions, feel free to ask and Ill help you however I can.