Why on earth would it be so front-loaded when its first few years are severely supply constrained, and in terms of appeal it's very much in line with the PS4 which wasn't front-loaded?
PS5 has a whole lot in common with the N64. Both are successors to systems that dominated their generation. However, both are destined to fall. You have to look at the factors that cause the numbers, and not just the numbers themselves. Going by the numbers, the N64 was the fastest selling system in its first 1-2 years. The most enthusiastic console gamers could not wait to buy one. However, if you looked closely at the time, then you might have noticed CD's were a clearly better choice over cartridges, especially for developers. An alert person would have seen the tides shifting, but you'd never have seen it if you went purely by the sales numbers for the first 1-2 years.
The main problem with the PS5 is that it's really only going to be popular in Europe. Japan PS5 sales will fall next year, because no one there is buying PS5 software. RoW sales behavior is not too different from Japan. In North America, XBox is arguably a stronger brand than Playstation. With Microsoft clearly putting in a lot more effort this generation, they are going to coax back a lot of 360 gamers who bought a PS4. That leaves Europe. PS5 will do well in Europe. It's going to lose a lot of ground everywhere else.