Riot, what was the design choice behind Aurelion Sol's E cooldown?

I just dont understand the design choice here. I would greatly appreciate some insight on why the ability has such a high cooldown for what it provides.

Some champions that effectively have a similar ability:

Kayn's E - 21 Seconds - Can freely navigate through terrain for a set amount of time with slow resistance in blue form Bard's E - 18 Seconds - Can not be disturbed through dash with the exception of a few abilities. Hecarim's E - 20 Seconds - Can exceed achieve high movement speed and navigate freely. Nunu W - 14 Seconds - Limited Navigation & Damage.

Aureleon Sol's E - 60 seconds *** - Can go in a straight line at a capped speed of 600, and can be disrupted by movement commands and any form of damage.

Wouldn't it make more sense for the cooldown to be similar to these champions? Even if their needed to be a trade off in the distance which the champion could travel as compensation. The E has the effective cooldown of an ultimate.

I don't think the ability is overpowered at all, and being a fundamental part of the champions kit it would make more sense that it has a relatively reasonable cooldown.

I'm not saying anyone is wrong, or the champion was designed incorrectly, but I would like some what of a explanation on the reasoning.

My suggestion:

1.) Make Sol's E - Shorter range, shorter cooldown, remove fixed movement speed. 2.) Alternatively Keep long range, long cooldown, but add a passive that lets his stars reduce the cooldown of his E based on champions hit. 3.) Alternatively keep long cooldown, long range, but allow for limited navigation but make it akin to a sion ultimate which can move through terrain with reduced damage.