Impaler is not a fun unit to play against in large teams. Its greatest strength is psychological: at SOME point in the game the enemy player will stop moving their com, will stop moving their jugg, or will get widowed. And they know it. It induces panic. I have to be CONSTANTLY clicking shit or otherwise alter my tactics in ways an impaler isn't supposed to influence. I can't spend 80% of my time making sure my units dont get sniped by what is supposed to be anti-static artillery. This doesn't apply to small teams or 1v1, but I've seen at least 1 high-elo 1v1 where units dying to impaler still happened due to inattentiveness. It can be frustrating.
Patrol does not work against this that well, and even if it did, that would still be kinda... not good. I believe one of the core philosophies of TA was large scale battles, and as Impaler demands constant micro to make sure your units don't get straight up deleted that Impaler does not fit well in TA philosophy.
I understand Impaler spam usually isn't effective or cost efficient, but I still feel it shouldn't have the effect that it has. It's anti-fun.
Now let me mention some other Impaler strategies...
- Impaler + widow is in most instances far superior to Ultimatum. An ultimatum costs 2500 metal and rarely makes cost. 3 impalers and 3 widows? about the same, widows are a lot faster and usually make it out. Then Impalers go for their risk free target. You may think screen can deal with this, but not if impalers manually target fleas outside of your notice... assuming you even have time to set up screen whilst manually dodging impaler fire
- Athena-Impaler ambush: Superintendant has used this a lot I think. Impalers have quite a 'soft' firing and hitting sound in proportion to their immense damage. As a result, someone sneaking in an Impaler next to a singularity reactor often isn't noticed until its too late (given they take advantage of radar dark spots)
Most of what I said only applies to big teams, but I know Impaler is a common complaint. A better description for Impaler would be 'anti-APM artillery'