I am into following the canon stuff when it comes to attributes and hierarchies. Let's just set a rule about a specific level of mastery whereby a fruit user can maximize its immunity, eg:
41-60: +1 durability to electricity but not to heat imbued into it
61-80: +2
81-99: +3
100: total immunity to electricity
This may look ridiculous at a glance but it's what it is for a rubber if applied physics and chemistry are involved whatever branch of science it is. Lol
Need I go on? Like Kakashi said, an opponent is expected to discover some mechanisms to counter or leverage on other skills in order to take the upper hand against, we got haki and other stuff.