DPS for tanks would only make sense if the state machine worked as follows:
1. Enemy spotted
2. Reload shot
3. Fire
4. Go to 2
Instead, it works like:
1. Enemy spotted
2. Fire
3. Reload
4. Go to 2
Basically, DPS completely ignores alpha damage, which is the most crucial part of the equation.
Moreover, DPS completely masks the effects of what happens when you increase the amount of tanks dealing damage. When you have 2 tanks opening up at once, the DPS doesn't simply just double; it goes even beyond that.
For instance, it takes an AT gun 4 shots to kill a T34. That means 3 reload cycles. If you put 2 AT guns on the work, that's still 4 shots, but that takes only one 1 reload cycle (that occurs in parallel between the 2 AT guns). That's 3 times faster, and a DPS calculation would completely ignore that.
Alpha damage is what allows Panther spam to be amazing despite the fact that singular Panthers are shit.
You can get away with DPS calculations for infantry, simply because the reload time is small, and the duration of combat is usually long (especially when cover is involved).
Yup I'll take alpha over DPS any days, which is why Jpz IV and Firefly is the most common TDs, followed by Stugs and M10.
My priority: accuracy>>alpha>>>cost>>>DPS. This is why Jpz IV and Firefly is the most feared TD, Jpz because of the awesome camo shot and Firefly due to lol alpha strike.