Simply no. Teleport alone makes games get losed/win. Not to mention turrets,shield .
Teleports? Id say more so the shield generator.
You dont need a flanking DPS to take care of the teleporter... make a pick or two, rush to the point, kill the rest of the team and then play "defense" and just pick off the stragglers as they come through the teleporter.
The mistakes people make is, instead of staying on point and defending, either NO ONE is capturing the point or not enough. So you have 2 people near the teleporter, and then they die because they get out matched, then you die because their whole team is back etc.
Id rather a Symm put up a teleporter than a shield generator.. but thats just my opinion