iphone hardware

iphone 6 caught in an apple logo loop yesterday. I'm not sure if my son had updated it or not, but at one point while it restored for a very short period of time, I did notice that it was running 10.2 (14C92). I chatted with a rep, who came to the conclusion that we needed to visit an apple store. The service rep at the store performed the same troubleshooting as was done the previous day without success, then brought the phone in the back. I was then told that it was likely a logic board issue, and that I could receive a replacement for $299. The manager then explained that some iphones may have issues while updating as a result of past damage. The phone has no visible damage, and had previously had no problems. When I commented that it sounded as if asked if he was telling me that the iphone 6 was not robust enough to withstand one of its own updates, he offered no explanation. We've tried different computers, cables, etc. itunes was up to date. SIM taken in and out, attempted all of the combinations with the buttons, etc. Any ideas?