Part of the problem with turbocharged gas engines is that they usually require premium gas and, unlike other engines that are premium recommended and can compensate for regular gas, if the owner uses regular in them it can severely damage the engine. This isn’t a problem with a turbo diesel.
All things being equal, the turboed 4 will generally get better mileage than a naturally aspirated 6 with roughly the same power rating, although it isn’t always the case for various reasons.