Stats in this game are displayed to you much differently than how they are used internally. The stats you see in-game are actually just a calculation of base stats and internal modifiers.
Your stats start off as base stats which never change. When a Wayfinder, weapon, or accessory levels up, it's power grows linearly. However, the stats it obtains through growth is distributed according to the distribution of the base stats, creating a power budget. All Wayfinders happend to have the same total power budget, and so all Wayfinders are technically equal in terms of stats.
After calculating your stats with the power budget in mind and weighting them according to the budget modifiers, we get internal stats. These internal stats are what the game most likely uses for calculations, like damage calculations, stats gained by various affinities, and applying buffs/debuffs. Then, the internal stats are mulitplied by their display modifiers to get your display stats. These are what the game actually shows to you.
The reason they go through all of this trouble can only be guessed at, but here's my best theory. Base stats are used because having an actual power budget to base all characters off of may be useful for determining balance. Internal stats are necessary because some items are weighted using the budget modifiers differently. Stats growing faster/slower than others due to budget modifiers creates stat complexity. Finally, the game uses display stat modifiers I assume because they want to round the stats to display to the player while keeping decimals somewhat intact. All of this though makes it very confusing for people just trying to min/max, so I made this tool.
TL;DR: Stats start as base stats, become internal stats, and are displayed as display stats. It's complicated.