I'm more referring to blocks broken per second. If your machinegun is capable of penetrating five layers of advanced armor, then you can get through the armor on most modern ships and do the highest possible structure damage per second. The problem with high alpha cannons is that they're not able to put out nearly as much block destruction per second as an equivalent machinegun, unless that machinegun is unable to get through the advanced armor layers on its target ship.
Armor is still extremely useful for high mass ships, but there is a very, very high mass dropoff point at which point enemy machinegun arrays are able to cut through it reliably, depending on the quantity of machineguns used by the enemy ship.
Well, the turret I am referring to IS a machinegun, firing ten times a second. That particular cannon is my 'medium' turret and it cannot itself penetrate 'five' blocks of advanced armor. That is not really it's job, it's job is to kill drones and similar small craft. To that end, it can crack a single advanced armor block while the armor still has an HP pool, or it can crack the armor and do a few systems blocks damage in addition, or if the armor is gone (or was never there in the first place like for most drones), then it will kill about eight system blocks in a row with each shot... ten times a second. There are few drones that will not be overheating Swiss cheese after a couple of seconds of attention from such a turret.
For dealing with heavy armor, I have my 'megaturrets', which 'can' crack five advanced armor blocks per shot, ten times a second. The actual number destroyed actually depends on a few factors however, such as whether or not the target ship still has it's armor HP pool, whether it has pierce effect, etc.. If it is out of HP pool, each of the two barrels on those turrets will punch through five advanced armor, with subsequent shots penetrating deep into systems, assuming they don't strike fresh armor. If the target ship still has HP pool, each barrel will crack two (and a half) advanced armor blocks, if it has HP pool left 'and' has max pierce effect going, they will crack only one per barrel while the HP pool lasts.
A ship carrying those megaturrets will typically also have ship fired weapons which will usually be an array rather than single or dual barrels, each of which will hit with the same power. We are talking now about titans however. Those megaturrets are far too big to put on smaller ships (they are well over 100,000 blocks each).
My smaller ships will typically have four of the medium turrets which are a tenth of the block count and (for a battle miner) a nice set of heat seeker swarmers.
[DOUBLEPOST=1444669920,1444668988][/DOUBLEPOST]To the OP, note that the last few posts have been kind of sidetracking talking about what people do or can do to get though armor. Most people do 'not' do this, which is
Azereiah's point. In both cases however, armor has changed the game. Versus those who have not made provision for cracking armor, having appropriate armor on your ship can make you 'much' harder to destroy. Versus those who 'have' built their ships to deal with armor, well, they've built their ships that way because of armor. Were it not for armor, likely they would be even more fearsome for some other reason.