the Relic, Dr. Octopus's arms reads:
Does this mean that a character with a higher printed range, have their range reduced to 4?

Nope. Dr. Octopus's arms grants a minimum range. It means that if the character's range is less than 4 after all replacements and modifiers have been applied the range will be 4.

Note that, even though you have 3 arrows you deal EE splash with what you have on the base

And to absolutely clarify: you cannot modify a min range

WoL Ganthet is pretty crazy with these.