Vision/view is related to how far that unit can see. (f.e dragonfly have 12 vision, which mean it can see 12 cell around it). While firing range is related how far that unit can shoot/attack. (f.e dragonfly have 8 range on its missile launcher, which mean it can attack an enemy units or building 8 cell ahead ). So, a unit usually can see the enemy with its large view but cant actually attack them since its out of their firing range, they have to be closer to actually attack the enemy. But there are some units that have small view but have massive firing range (f.e torrent, mammoth, Solaris(un-upgraded) and etc.) These type of units usually need a scout to harvest its max potential