Regarding the problem with my phone (reboot loop after losing signal and restarting), the service center say they need to change the board... will take 2 - 3 weeks. Considering the phone is new and problem occur within 3 days of usage shouldn't they be giving me a replacement instead of repairing ?

Google Experience launcher can be found on XDA forums. Although I would prefer Nova launcher anyday.

For my earlier boot loop issue I had given my phone to Sony Service Center. Its already two weeks and now I get a call from SSC telling me that shipment is delayed and they can only get me a replacement in 2 - 3 weeks.

Is it wise to send the original for repair considering it was only 3 days old when the problem appeared ?

This is seriously bad that too for a flagship. I don't know what to do