Here’s an example (with fake stats and super over simplified formulas) to answer your question. Let’s assume your recursion does 100 card damage.

(weapon damage) x (splash) = final damage

(100) x (1) = 100

Without any gear or skills or GR the the 125 splash will do more damage.

(200) x (1) = 200

Vs

(100) x (1 + 1.25) = 225

If we make up gear stats to make this easier, say you have an artifact with 30 splash damage, and a class mod with 30 splash damage.

100 ASE

(200) x (1 + 0.3 + 0.3) = 320

125 Splash

(100) x (1 + 1.25 + 0.3 + 0.3) = 285

See now the weapon damage ASE is better. So let’s add skills into it that raise weapon damage by 80%.

100 ASE

(280) x (1 + 0.3 + 0.3) = 448

125 Splash

(180) x (1 + 1.25 + 0.3 + 0.3) = 513

Now the Splash ASE is better. So that answers your question of why gear and stats matter, it changes the outcome.

So why does the outcome change? Becuase when 2 numbers are multiplied by each other raising one number will yield less increase than changing both numbers

(150 x 50) is less than (100 x 100)

(101 x 99) is less than (100 x 100)

The closer the numbers are to each other the higher the final number will be (assuming you’re increasing the size of the numbers obviously).

This also assumes splash on the recursion works like splash on other guns which in not 100% about, but others say it does so I believe them.

If I made any mistakes, the point still stands, I’m just tired.