It's probably safer in LMP Coupe 99% of the time, but if there's inside fire in the cockpit like in the CLM last year at Fuji or something, then you'd rather be in open vehicle you may quickly jump out of.
Of course fire in GT can be even worse, if you've got to climb to the other door for some reason like here below. At least in LMP there's not huge space between door, even if the seat is not entirely centered like in open wheeler
