The PC Engine GT/Turbo Express was ahead of it's time.... the LT was light years ahead of it's time.
Regardless of sales, releasing something like the LT in the US back then would have turned heads. Alone, a move like that probably wouldn't have been enough to change the fate of the Turbo Grafx, but it may have drawn enough attention to NEC to help get some of the other issues back in line.
The fact is that console wars have been around long before NEC was in the game. Making people want the system (and actually buy it) is always the key to victory. There is no doubt that the LT would have made people want it. Affording it would have been the other issue.
The Express, as much as I love it, wasn't enough for the general public to change the fate of the system. And had NEC got all of the 3rd party support in the US that they did in Japan, the Express would have fared better, but price (even for the express) would have still been an issue.
PCE GT:
US Turbo Express:
PCE LT: