Swim Bike Run Ratios in Weekly Training Plan

I have a general question regarding the relative amounts of swimming, cycling and running I should do in training to get the best performance on race day.

Let's say I'm training for an Olympic distance race, whose component parts are 1.5 km swim / 40 km cycle / 10 km run. If I want to be balanced about my training, in a given week I might decide to do 3 x the distance in the race, in each discipline, so this would be a total of 4.5 km / 120 km / 30 km. Let's call this a ratio of 1:1:1.

However, some people have commented that I should do relatively less running in order to avoid injury. Others comment that it's better to do relatively more cycling as this is the longest part (in time) in a triathlon. Others would put more (relative) importance on swimming. Obviously if I'm weak at one then I should focus on that more than the others in order to improve more, but for the sake of argument, what's the base case I should be aiming for?

I hope the question makes sense!