I guess he meant relative relevance really, in your examples:
10 w.atk + 600 atk = 610 dmg = 915 c.dmg = 15 + 900 --> 98% c.dmg from STR
1000 w.atk + 600 atk = 1600 dmg = 2400 c.dmg = 1500 + 900 --> 37,5% c.dmg from STR
10 w.atk + 1500 c.atk = 10 dmg = 1515 c.dmg = 15 + 1500 --> 99% c.dmg from DEX
1000 w.atk + 1500 c.atk = 1000 dmg = 3000 c.dmg = 1500 + 1500 --> 50% c.dmg from DEX
Even at 100000 w.atk
100000 w.atk + 600 atk = 100600 dmg = 150900 c.dmg = 150000 + 900 --> 0,6% c.dmg from STR
100000 w.atk + 1500 c.atk = 100000 dmg = 151500 c.dmg = 150000 + 1500 --> 1% c.dmg from DEX
I guess something like 5000 w.atk would be the usual end-game value, in that case we’d have:
5000 w.atk + 600 atk = 5600 dmg = 8400 c.dmg = 7500 + 900 --> 10,71% c.dmg from STR
5000 w.atk + 1500 c.atk = 5000 dmg = 9000 c.dmg = 7500 + 1500 --> 16,67% c.dmg from DEX
In this example, and considering average damage alone to be the relevant factor here, DEX would be favored for crit chances>50%. Otherwise, STR would give a better DPS output.