OP didn't say anything about reducing fat intake. Aspartame is a sugar substitute, OP talked about switching from sweetened beverage to unsweetened beverage neither of which has any fat. OP also said "your teeth will thank you" which again is an association between sugar and tooth decay, of which fat plays no part. Fat is a nonsequitur here; the linked article is about a sugar substitute.
The nutrient density of desserts is magnitudes higher. Carbohydrates, protein, and fat are the primary nutrients. You must mean micronutrients, i.e. individual amino acids, vitamins, and minerals. Of these, the snickers bar does quite well with amino acids thanks to the peanuts, but yes, a serving of strawberries will give you vitamin c which the snickers won't.
However, that single vitamin is the only real difference in micronutrient quality!
The fruit and candy are both negligible 2-10% amounts for the remainder. They're also very similar on mineral content, with the candy providing 8-10% dv on 5 minerals, while the fruit provides 7% and 29% of two minerals, the rest negligible in both, averaging 5.6% dv for the fruit or 7.6% dv for the candy across the ten minerals.
I already addressed water mass and caloric density, but for completeness I will say again that you're getting these very comparable amounts of micronutrients for a tenfold caloric difference.