Not sure about auto tune but I think that's Husqvarna . Stihl has the Mtronic. Auto adjusting for conditions. Altitude, humidity, temperature and even less than clean air filter. I've been running 3 stihls with no problems so far. The oldest one is over 2 years old and the newest about 4 months. You mentioned an 18# 70 cc saw,my 462 is 13 lbs, powerhead only.
EDIT. Stihl has come out with a fuel injected saw but not available in th US yet. 500i,80 cc
046 full of fuel and oil 20" bar 76.5cc.. Feels really nimble and def not rough on the ol back or arms all day. But for a super lightweight all arounder id recommend a 346xp or 026/260/261.