Pound for pound its true that smaller ships have more slots per logistics than larger ships, so at first it can seem like a no brainer "why not just use tiny ships all the time?". And that is a viable strategy especially around military starbases which boost each ship.

However, once you understand the interaction between defense and weapons you realize where large ships become really strong.

The key concept is: Your full defense value applies against every single attack made against you.

So if there are 15 tiny ships firing at my large one, my defense can soak each and every single attack. So if I have a 40 defense against a tiny ships 8 attack lets say, practically speaking my large ship is only taking 1 damage per hit (as you always take a minimum of 1 damage). Combine that with the durantium hp booster taht gives you +20% more hp (which on a large ship is a big deal), you have a juggarnaut of a ship.

I find a great combo is to combine an Escort Role Large ship with a fleet of tiny Capital Role ships (yes I use capital, its more straightforward in its interactions than the Assault role). All of your tiny ships blast away to their hearts content, while your tank just soaks a tremendous amount of punishment with only minor damage to show for it.