I still say Unleashed isnt about speed, speed, and more speed. Yeah you can go through on the "default" path, but think about how fast you could run in classic 2d Sonics or Sonic Advance 1. You could still stop pretty easily, and there are too many springs the "player' missed and other visible paths in the trailer of the stage for you not to have to slow down and do some platforming.
Also dont forget Sonic 3 had many "on rails" sections were you really didnt have control of Sonic until you came mout of the circuit. Case in point, the water torrents and loops in Hydropolis. Or even Sonic 2 with the Chemical Plant Zone pressure tubes.
Just to prove my points:
There had to have been a seperate path to take from the start, those rings arent there for nothing. So evidently thats not the start of "High Europe".
If you just go blazing through the level, you'll most likely miss this alternate jump path, either that or you'd need a good amount of speed to hit the balloon and make the higher path.
From that balloon bouncing path, you'll most likely fly across to hit that trick ring that should launch you to either another path or just give another boost of some sort.
Another spot where the player zooms by, yet could've slowed down, took advantage of the wall jump...
And then hit the spring on top of the building
Instead of sliding under the platform, jump across the balloons and take the high road
Behind the back moment, yet you can move to the right and take the high balloon path instead of just going straight.
Here there is a split path. The one of the right most likely leads to...
The spring path on the right.
Theres another section after that to take an alternate tunnel path
Dunno how you'd get to the spikes since the trailer jumps around abit, but the spikes are there for a reason.