Isn't adding 1+ dex but adding 30 hand encumbrance contradictory for tentacle arm mutation?

Considering the fact that tentacle arms add dexterity but increases encumbrance, doesn’t the two cancel each other out? Shouldn’t one or the other stats be removed for redundancy? or is my math off?

but you get more melee attacks or some stuff I dunno. Seems to me the tentacles (especially 8 tentacles) even with guaranteed hits still don’t actually do that much. seems like the tentacle number doesn’t matter, it’s still 50/50 whether you attack with (1) tentacle or not at all.