The gearbox issues I think were mainly for the PFL A45 and were mostly fixed with the FL A45. The main reason I say the gearbox and 4Matic system is that the FL A45 still lost to the PFL RS3 in a drag race (and rolling starts too) even though it had more power and people were blaming those 2 things on why it loses. The FL RS3 then made the lead even bigger. The A45 always was the better handling car compared to the RS3 but the A35 is competing with Golf R, Civic Type R, Focus RS, BMW M140i etc, and there are some great handling cars there. I'm unsure what you mean by the tech being more effective in the A45, I had a 2017 C class for a week and found the tech to be 1 or 2 generations behind the S3 in terms of design and capability.
From my experience A45 lost to pre FL rs3 off the mark because the AWD system was too FW biased and slow to move the power to back wheels. Add to this the pre FL rs3 (with the smaller turbo) had a healthy dose of torque from about 1800 rpm. while the a45 needed to wind up more before it was on song.
My reference to tech was all the functionality I use in both cars, and mine aren’t daily drivers so I probably don’t use a lot of it. But thanks for giving me a chance to have a whinge.
Drive Modes - the a45 has 4 drive modes, eco, sports, sport + and race (plus individual, the custom mode). You have them at the turn of a wheel on the console. In addition suspension and exhaust could be activated by addional buttons on the dash. Very quick and easy to pick a mode that suits your mood and driving conditions.
The rs3 effectively has 2 modes the economy and sport. I live inner city, so in sports mode my car never gets past 3rd gear. The fact that you have the cycle through a menu every time is a pain. I’m not even sure what happens in the AUTO mode.
The a45 will remember Your driving functions settings for 4 hours. So if you’re in and out of the car you don’t need to reset everything and remember turn off stop/start off.
When you set your radio favourites in the Merc, it just displayed the favourites, not so in the rs3 where you need to go back to menu to call them up.
The rs3 navigation system is laggier
Another useful ‘tech feature’ I used in the a45. You could display large gearbox and engine Temp gauges on the MMI screen. As well as giving temp they changed colour when they were up to temp, so easy to see at a glance.
Whinge over!