As much as it is OPed, if it's ranging a BB1 then there's something wrong with the BB.  Any CL+ stands a fair shot against it in a 1 vs  1 situation if it carries a scout.  Its slow speed should keep you out of visual range but 90% of the blitz CL+ players run up to it because their guns are too small or they don't have a scout.

It also has poor gun arcs (compared to the DDX or NDD) so if you get directly behind it for example, they are likely to turn to fire giving you a larger target to hit at that moment.

In the case of fighting it with a DD, using speed and rushing it is probably the best solution. 

The main factor that makes the Leone OP is the skill of the player. EOC Leones are meant to play like a BB1 - engage at long range (at broadsides, due to the aforementioned gun arc problem), disengage when superior numbers attempt to rush. The powerful setup of 4 6" singles negates the downside of the rest of the RM DDs (fast, small, but undergunned - witness the poor gun layouts of the next three DDs). It's a tantalising option for CL/CA players (barring Capitani Romani) due to the fact that their spreads are simply awful using the EOC.

A Leone can be easily countered by having 2-3 fast DDs surround it and pepper it to death, or just sneaking up on it and blasting the hell out of it. CVs will also find it a nice target due to the weight of its guns inhibiting both speed and defense. One or two torpedoes will easily take care of it.

Like any ship - if you find it to be overpowered, then play it or closely observe it and look for weaknesses.  Now I'm not saying it's not OPed - it is but there are ways to fight it that can at the very least allow you to do significant damage to it.

It is particularly unfair in the early - middle parts of the game where other players engage dand the Leone player can sit back and fire without getting hit.

But it is slow and has poor overheat damage.  A torp ship should target it.  And as I said before in regards to CL+ that engage it - a scout will make a huge difference.  Instead of chasing it, make it chase you.  I'm always ever so thankful when the larger ships come one by one and close enough for me to see them.

I will never understand Cpt Romani players.  They can use the EOCs and a scout but most choose no scout and pack on a bunch of armor.

The leone does NOT have the range of a battleship. Thats been proven by the release of actual numerical range.

The Leone is very different from most destroyers and especially Tier 1 Destroyers. Other destroyers are nearly indentical, and have ranges of about 1500 with 6inch guns. That may seem odd but the special EOL 6inch guns were ment to be a secret high velocity gun during world war 2.

the Leon is balanced as it has THE WORST weight, speed, and even the only dd1 that has a 50% speed decrease, unlike most ships which only lose speed at 40% hull points. A few hits and its crippled.

Even if you do equip the 6inch guns, you cant equip secondary weapons due to weight, and because its a destroyer with limited weight you cant mount skilled sailors.

Bottom line, the Leone DD1 has long range guns AND NOTHING ELSE. Get over it.

Don't forget the dmg he can make... 700 per shell...