I think i just found the Artifact Upgrading Algorithm in Genshin Impact
So i think the artifact enhancement algorithm are like this, the lower substats you have the more chances it will level up, and the more higher substats are the lower chances it will level up, but!! if the high stats are success to level up such as cdmg 7.8% it will goes really high into 30% or even 40% if you are lucky enough to level up that cdmg by multiple times.
So basically you just have to choose which one you need to upgrade to 20, and recycle the other for the new artifacts such as Bloodstained, Gladiator, Noblesses or Wanderer's Troupe on the crafting table, until you get the artifacts that really worth to invest such as 7.3% Def 4.1% ATK 5.4% CDMG and 299 ATK. So you will have higher chances to get 25% CDMG or so.
Timestamps:
00:00 Intro
00:24 Theory
01:06 Testing Theory
03:59 2nd Artifact Upgrading
05:12 3rd Artifact Upgrading
06:27 4th Artifact Upgrading
07:37 Outro