You call maintaining a car scientific? Famous slogans? Non of us were born to maintain our cars on this earth so keep the childish remarks to the side. If you've invested a million rupees in something, atleast take care of it properly.
I don't know what the issues with the head gasket were that your mechanic worked on for but since you said it yourself that the overheating issues came after that particular work done, the only sensible answer was the engine consuming the coolant and a bad case of repairing work done by the mechanic on the head resulting in the overheating issue. Removing the t.stat is only gonna mask the original problem. I gave you the possible causes of the problems and shared a link so you can read that and understand it. I'm also gonna skip on all the other immature statements you gave. If someone tells you you've done something wrong, look into the matter and don't get all kamikaze.
Regarding the workshops in karachi, you can use the search bar. Its there for a reason on the main page and in the topics itself. I'm from Islamabad so I know a few here that actually have the proper equipment and tools (and most of them are linked to PW) but guys like saboor may know where to find workshops that have proper tools in Karachi.
1) Because at that time, I wasn't very well informed about the m13a to diagnose the problem stated below
2) The engine had started eating up one of the coils every week or so. The problem started when the driver sprayed water+oil in the engine bay while the there was no engine cover over the coils.
3) M13a was always gonna be in the shadows when compared to the M18. We found a half cut with low miles and swapped the engine+box. Ran the stock ecu initially but later swapped that too.