Actually, that is the much more common organized military organization's uniform.
The soldiers looked similar to the rest of western Europe, expect the Spanish who ALWAYS look different than ANYONE else. In eastern Europe, other eastern influences made the armour and arms take on a different look.
The Scots were one of the advanced nations of western Europe, even being called on for assistance by larger fellow nations.

The Scots were known and famous for their "saffron shirt," even though historians debate:
1) Was it actually saffron dyed , or was it just a yellow dyed shirt (what we would calll faux saffron)?
------ Some argue that saffron itself was heavily grown in Scotland, esp. as it was likely warmer there in the 800-1100/1200 than today (Greenland has farms with plowed fields from that period in what is now permafrost). So, actual saffron might not have been rare or imported in Scotland, just reserved for the domestic usage.
2) What shade would they have been? Mustard/Orange-ish brown? School bus/DOT yellow? Lemon yellow? Pale yellow?


The belted plaid is first recorded with certainty in the 1590s, almost 300 years after the Battle of Bannockburn.
The Woad/blue face paint was a feature of the Celtic peoples that fought the ROMANS in the first centuries AD. It was nearly a thousand years out of date for William Wallace and Robert Bruce.

The "revisionism" now is a return to a more traditional interpretation of history. The idea of kilted warriors emerged in the 19th century Romanticism writers, such as Sir Walter Scott and popularized enough to reshape popular imagination. "Braveheart" added the blue face paint and a NEVER before seen form of belted plaid in 1995. The costume person was hired SPECIFICALLY because they ignored tartans (see DVD commentary), though they seem to have also thought of Scotland as a severely backward and shabby third-world country . . . all of which has little to do with reality.
So, we have the fact-based histories, then 19th century revisionism that dated "modern" kilt ideas WAY too far back, then another revisionist layering after Braveheart (among popular writers, not historians), and now a "revisionist" movement that is actually quite close to 18th century and earlier writers . . .


The leine croich was replaced by other garments in the 1500s, as armour was replaced all over Europe. The fued-warriors wore practically modified variations of their normal civilian clothing.
In the 1600s and 1700s, the Clan Wars take the form we think of with swords, massive claymores (more symbolic than effective), muskets, and later with baskethilts and so forth wielded by kilt-clad warriors.


That said, there is plenty of evidence for tartan patterns used in fabrics from scraps and remnants found in digs. So, I wouldn't say that tartan didn't exist or wasn't used. Rather, I would say that it wasn't the main symbol used for Scots in war. THAT was the "saffron" shirt.