Can datalog and check the readings.

Some can... it depends on their experience and familiarity with the particular engine.
Conti cars 4man normally have higher skills for this because of the complex and weird problems conti engines have.

However if i was diagnosing a Myvi... and since there is so many Myvis around.
I would first datalog a good problem free Myvi vacuum, MAP, O2 reading, Injector duty cycle, ignition timing, cam angles for example.
Then compare with the problematic Myvi and see if the readings are similar or way off.

I've my own scan tools, and those workshops normally have better and more expensive scan tools compared to mine.

If using one off, it's expensive lah... I'm using Thinkcar scanner, the cheapest one.
Not mistaken cost RM 100+ and there is annual subscriptions fee based on function and car brand.

I'm in Melaka

Thinkcar Thingdiag mini
Plug to car OBD2 port and connect to the Thinkcar app on phone.
Additional purchase is annual subscription fee based on the car manufacturer and also function you want.

Yes, can real time monitoring.