1 - light weight model to help increase club head speed for anyone currently driving less than 220 yds.
2 - most forgiving for most players
3 - more penetrating flight, less spin for most players
4 - most low spin design to help those that generate too much spin even with low spin shafts
Definitively different purposes for each although there may be close calls. That the TS1 and TS4 came out later has nothing to do with replacing the TS2/TS3 models. Each has a place in the lineup. Different than other vendors where the X4 replace the X2 but now has been replaced by X6.
Now more than ever, one needs a fitting to find the right model for one's swing.

Bought a TS1 Friday and played today, flew the creek on #6 for the first time ever! This baby is LONG! Speeder 35 shaft for this 68 year old man, LOL!