Difference between tanks and infantry and artillery is. Artillery surprise one shot wipes anywhere on the map. And when spammed kill anything and everything.
Infantry and tanks require positioning and combined arms. Artillery promotes turtling and one shot no skill bs.
not necessarily on so many levels...
some tanks and infantry will surprise one shot targets: the brit and OKH snipers to each other, nades over shot blockers, lucky roles on tanks, stiger, AVRE... i'm sure there are others.
artillery can only hit within its range. how much of the map that covers depends on the map and the artillery piece and is subject to balance changes.
infantry and tanks do not require positioning or combined arms. volk blobs, riflemen blobs, gren blobs, shocks, cons, guards, jaeger light, stroopers, etc can all be blobed and several of those mentioned counter both infantry and vehicles. tanks are quite blobably as well; i just got out of a game where a brit player was blobing cromwells and i had a game last week where a soviet player blobed su-76s. any of the baseline mediums will blob and counter both vehicle and infantry though.
artillery does not always promote turtling and if often the only way to break a turtle. all artillery (iirc) must be stationary to fire though and that does tend to promote slower gameplay because you have to stop to fire. the best counter to artillery though is getting close to it.
the best way to deal with one shots is to make the <80 damage portion of the AoE smaller and the >80 damage portion bigger so that artillery deals more consistent damage without wiping blobs. relic seems to like the wipes though.