Do 5-star artefacts with 3 or 4 substats have the same potential?

When optimising characters, the substats of artefacts play a defining role. Substats cannot be the same as the main-stat. Every 4 upgrade levels an artefact will receive a random substat if there are less than 4, or improve a substat if there are already 4. 5-star artefacts start with either 3 or 4 substats.

When a 5-star artefact starts with 3 substats does it have the same potential as a 4 substats 5-star artefact or does it lose out on potential because it misses out on one improvement?

Your assumption is correct - 5* artifacts with 3 initial substats has less potential than 5* with 4 substats.

How it works (based on community research):

There is a set of predefined values for each substats - 4 different values (they are called "tiers" in the table below), they are also different for artifacts rarity - 5* Tier 1 is better than 4* Tier 1. Initially, your 5* artifact receives either 3 or 4 substats. Then it receives additional substat on +4, +8, +12 +16 and +20 upgrades, 5 upgrades total. For any 3 substats artifact the first upgrade will always add missing 4th substat, then each next will add additional value to one of the 4 substats. Additional values could be of any tier, so T1 substat could receive T4 upgrade or vice versa.

So, 5* 3 substat artifacts will have 3 + 5 = 8 substat values total, while 5* 4 will have 4 + 5 = 9.

This is the table with all possible substat values:

Source - this reddit post

P.S. this game is not some highly competitive PvP game, so trying to get the best possible artifacts just not worth it - you can clear all the content with all average teams with any average gear.

• Regarding your P.S. since the only limit on running the Artifact domains is Resin (aka Time) there's no reason to not strive towards ideal artifacts. Even if you whale and buy 6 resin upgrades every day RNG is still going to be the limiting factor. OTOH upgraded artifacts can be fed to others w/ about 80% efficiency, so even if you upgrade a good (but not great) artifact, you can then feed it to the great artifact when you eventually pull it. Commented Jan 19, 2021 at 16:18