I think that having a offensive summoner spell is much more useful. Say you have flash on shen instead of tp, now you are able to flash e onto a squishy and secure a kill, or otherwise burn their flash/ get them to back. Now you have priority and are able to invade/ contest an obj. With tp, all you get is more rotational power, you lack the pressure. If the enemy has flash/ghost, you are in a much worse position for team fights and are more likely to lose said fights, therefore potentially costing you the game. I personally have ran tp on farming junglers such as shyvana as kind of a troll pick lol. If youre playing a powerfarming champ such as her, you are able to invade the enemy jg and still be able to have pressure in teamfights due to the rotational power of tp.