The thing is, the Colossus is definitely *not* free as it is costing you a whole perk and a metric s-ton of minterals + a little fleet capacity. It saps your ability to win wars (outside of fortress planets), where ID leaves you influence to get more resources to win wars.
Edit: This presumes more early game conflicts with ID, obviously the Colossus saves late game influence.
Yes, but ID also costs a whole perk. So in that regard both are equal. And you bring up the mineral cost. I don't know your lategame economy, but in the later stages of the game I have more minerals than I need. But it seems you assume that I actually build the thing. No, all I need is the TW CB. With enough time and minerals I will build it, though, for the fun of accelerating genocide, but it isn't necessary. I don't think this is an issue at all.
Actually, ID also isn't free of its economic problems: grabbing territory in the early stages also costs minerals, which heavily strains your economy. Especially energy for upkeep can become a problem until you can build up some good energy planets. It usually takes some time until your investment not only pays off, but also generates profits. And until your situation is stable, a FP or an Advanced AI just might attack when you're not ready. Compact empires are not only setup faster and easier to defend, but also have an easier time making some friends for the time being. Growing too fast (especially through conquest) will isolate you diplomatically.
It all boils down to this: The goal of the game is to achieve a complete victory. We are just disagreeing on the best timing of when to choose the perk to do it.
ID is a quick landgrab in the early stages. You just hope that you don't run into someone who can ruin your day. The Colossus is the ultimate landgrab in the late stages, where you ruin everyone's day. For me it is the safer and thus superior choice. ID is great if it works, but as I said, it is a risk when you don't know who exactly is around you. You're not invincible early on.
Wide means more minerals so just make two or three fleets and station them near the border systems? Make a bastion and station them at the bastion, it actually makes a huge difference.
Secondly when it comes to conquering your next door neighbor are you really going to wait 100-150 years until you have colossus? If you have an equivalent fleet and ID you can have 20% more of his stuff now. Down the line you will have more tech and more traditions unlocked.
Wide means that you are unable to react in time should something go the wrong way. Wide means more territory, that means you need more minerals and time to develop everything. Building three fleets takes longer than building one fleet. Growing too big too fast is a risk.
And the answer is no, I don't wait 100 years until I eat my neighbors. But I gladly wait 100 years until I can declare Total War and eat half of a federation in one go. ID will let you take 20% more, TW CB will let you take it all with a 100% discount on influence cost and without having to wait for the war to end.