First of all:
TCD is the display. TCU is the control unit inside the bike.
Secondly:
Any change in Tune done on a connected bike is reflected instantly in the bike, even if you move the slider in the app during the ride. So if you ride, the app's connected and you increase the Support from 20 to 60% in the current mode using the app, you'll instantly feel the kick from the motor. Yes, Mission Control overrides the manual selections.
Smart Control: It works online, too. If you set, for instance, that you want to ride for 50 miles with 1200 ft elevation gain and you want to end your ride with 10% battery left, it will be instantly transferred from Mission Control to the bike: actually the app and the bike continuously work together as long as the app is connected. You will see unusual layout of the Support Mode on the TCD display with Smart Control: two upper bars at the right hand side will be "lit".
You are told your e-bike is "2x you!" It is not exactly that. "100% Support" means it is 1.8x you, or 180% assistance. Let me explain that:
The Specialized 1.1 motor has 0-180% assistance (translated to 0-100% Support in Mission Control). Now:
If you are in 100% Support in MC (full Turbo), each Watt you input into the cranks is supported with 1.8 W by the motor. Let us say you are pedalling with 100 W of your own input. When the Support is set to 100% in MC, the motor will give 180 W of assist power for your 100 W leg input (you are producing 280 W together). If you pump up 200 W of yours, the motor should "revenge" with 200 * 1.8 = 360 W of power. But you know the 1.1 motor can provide up to 240 W maximum only. What gets? However strong you are pedalling, the motor can assist you with 240 Watts, and not more.
Then, there's the second parameter to be set in Mission Control (Support % is the first one). It is the Peak Power % (0-100). The Turbo mode example above assumed the Peak Power is set to 100%, or 240 W motor power. Now, let's look to some Eco (level 1) mode.
Let us assume you set the Support to 30% and the Peak Power to 30%, too. The Peak Power of the motor gets limited to 240 W * 0.3 = 72 W. Under no circumstance will the motor assist you with more power than 72 W for this setting. Now, you have set the Support to 30%, too. The Vado SL becomes 0.3 * 1.8 = "0.54 x you!":
Input 100 W yourself, the motor will help with 54 Watts. Input 200 W, and the motor will help you with 72 Watts (240 * 0.3). However, if you input 250 W, the motor will help with the same 72 W (not more) because the Peak Power has been limited to 30% of the max motor power of 240 W.
Your observation that modes 1, 2, 3 (Eco, Sport, Turbo) are very similar to each other in your situation is correct. You probably pedal hard and the motor gets "saturated", not being able to help you any more. One of TCD screens shows Rider's Power: How much do you typically input into the cranks yourself?
A good advice for a strong rider is to dramatically reduce Support % and Peak Power % at least for the Eco mode: It ensures very long range on the battery.
I hope that helps.