I recall this coming up during the testing of the 146 in XP12. It is expected that the TGT will peak out of limits if the throttles are very quickly advanced from idle to full power; however, I do agree that the TGT peak is quite excessive when this occurs (although there isn't any data out there to confirm/deny that).
From the discussions I had with the development team, the high TGT peak in this instance is predominantly a side effect of having the engine simulation accurate throughout their normal range. So if the throttles are advanced at a normal rate, the engines will behave accurately and the TGT won't go out of limits. I'm unsure if the needles should be able to rotate 360 degrees, but again, it's one of those things for which there is no data/reference material available for, as no one wants to be overheating the engines on the real aircraft.
I will, however, raise this on our internal bug tracker for the development team to take another look at ahead of a future update to the 146 XP12.
Mark - Just Flight