will i be having quite some trouble if i have no attacks with impact on them?

how often do people use lists with armour?

No armour has been the meta for a while now. That might be changing what with the new factions getting their heavy slot filled and new objectives coming out. I don't expect you'll have too much trouble.

There are some generally good units that work well VS armor, even if they are not dedicated to it. From the top of my head, DLT Stormtroopers have impact 1, Tauntauns have ram 1 in melee, AT-RTs have surge to crit... and all of the sable - wielders are pretty effective too (jedis the most but Darksaber Sabine too...). Of course is not the best solution, but it's something to have in mind.

If you play imperial, you will prob not need any impact at all with all the criticals and aim tokens. If you plan to face alot of vehicles as other factions then yes, you should get alot of impact. If you only bring a little impact, you won't have enough to down a heavy before round 5-6 anyway.