I have a Euro market 190e 2.6 M103 engine. This car was exported from the channel islands to the U.K. and then to Australia, The car has no Cat or O2 sensor.(wiring for O2 sensor in place). It features the rotary EZL switch as mentioned above in your posts. My car suffered from lack of pickup power also. Had the fuel mixture adjusted a little bit richer and this improved things at the expense of consumption.

According to a Bosch Injection specialist I took my car to, by installing the O2 sensor, this will improve consumption and engine performance - depends on the cost to do this. As my car doesn't have a cat and also features dual engine pipes to the first exhaust muffler, installation would require some extensive work, so maybe not justified.

Settings for the EZL switch. S is for premium fuel - 95 Ron and above. N is for lower quality fuel 91 Ron. The EZL switch was designed for use in countries with some really crappy fuel and adjustments accordingly. The higher the number the lower quality fuel to be used - right down to 89Ron.
According to the user manual. Using the S setting with low octane fuel can damage the engine. - so make sure you set the wheel correctly for the type of fuel.

Cars not fitted with the cat can use unleaded or leaded fuels. Cars with a cat must use unleaded.

Getting the fuel distributor tuned correctly makes a big difference to performance. The coil can affect performance also. Only use Beru or original MB leads cap and rotor. NGK make the equivalent non resistive plug for the M103 - MP6ES.