TSD is basically Shotokan karate with Korean names for techniques instead of Japanese. The patterns are those of Shotokan with little bits slightly changed ie a kick put in.
Actually, if you take into account the way the energy is built up in the two arts, they are very much different.
Punches, for example:
In Shotokan they have the artist in a basic front stance. They then step their back foot in, so it touches their other foot, and then out, so they wind up in a front stance, and they throw the punch when their back foot becomes their front foot. (Basically, they make a "V" motion with their foot)
In TSD, from a front stance, the artist drags their back foot slightly and keeps their hip slightly "behind" their body as they step forward and then they throw their hip and foot into the punch at the same time.
Different ways to produce energy with little effort, same result!
Same thing with kicks...for example:
In Shotokan, a side kick has you facing the target in a side stance...you step forward (or stay in place) and bring your knee towards yourself, lean back a bit and kick outwards.
A TSD side kick has you facing your target in a front stance, then you turn completely sideways to your target with your leg chambered all the way up in a ready position. You then release the kick, but as you do, you turn your body and your standing foot so you are facing the complete opposite way from your target.
Also, Shotokan stances are much, much lower than TSD stances as they believe their balance comes from being lower.
These are but a couple of examples of the differences between the two arts. They aren't different just because they use Korean adjectives to describe the moves instead of a Japenese adjective. Or one art places a punch in place where the other art places a kick. That is trivializing the differences between the two arts.
You can say all of these types of "hard styles" of martial arts are "similiar", but indeed they have many differences. Granted, you are correct, to the naked eye and untrained artist, they may indeed look very similiar. But in reality, they are very, very different as they all have their own ways of "gathering energy" and changing stances, doing their forms etc.