It's inappropriate to consider artifacts – anyone can have them, or they might not have them at all – we're looking at raw skills.

It is appropriate, precisely because they can be present, and with a high probability.
The opponent's artifacts ("anyone") don't affect the situation at all. Although, I'll take that back – there might be an artifact that gives a bonus to luck. But I'd rate the probability as low, unless we're playing against a Necromancer and need to consider that they might try to assemble a class set.

Elven Luck with its additional 25% bonus should also be disregarded – this is a bonus from a completely different skill, not from a specific skill unit – the skill tree on the first page shows that Elven Luck is present in the entire Luck line.

Elven Luck must be taken into account because it increases the value of luck as a whole (albeit not by much).