2 - Whilst its munchy as all hell, the Levi takes full advantage of things like bracket firing and the like. It's also seemingly designed with a bit of brains.
Not exactly.
The Leviathan was designed with Battlespace in mind. Thus it looks a lot like the new ships in TRO3057, FM:DC, and FWL. So it has a big reliance on conventional weapons and random usage of capital weapons. Armor is moderate and they were happy to use 2/3 thrust.
The Leviathan II was designed for RS:AT2. So it uses the AT2 rule set and gains the monolithic armor and tiny cargo bays of the FM:LC, FS, and CC ships. The NL55s and MNPPs aren't about bracketing because that came years later with Strat Ops. Instead it is about getting as close as possible to that magic 70 points of damage per bay at extreme range. Actual bay choices are about expanding on themes started with the Leviathan I. As for the 300 fighters? It is what the cool kids were doing after the Thera. Also note the lack of Small Craft as the ships of the time had a tendency to be min maxed.
The Leviathan III tries to make use of the modern post Strat Ops rule set while carrying the baggage of 20 years of history. A clean sheet design would make some very different choices.
Some of the rule choices in Strat Ops were made with making the TRO2750 ships viable. The McKenna was a big winner. For example, because the Leviathan II mounts a couple of paired NGRs and NAC30s the McKenna actually out guns it at long range.
That sort of puts the hodgepodge that is the Leviathan into perspective. It was less thought out but rather benefited from the luck of the draw when the rules changed. It could easily have suffered like the Nightlord.
Arguably the McKenna was more thoughtfully designed even without construction rules. The Small Craft Bays and cargo space shows the designer in world and out was remembered that WarShips spend most their time hanging around and patrolling, not fighting. The AT2 and TRO3057 ships tend to ignore this and are purely designed to fight on a table top.
For this reason I have a lot of time for older ships like the McKenna. Its biggest weakness in the modern era is lack of armor, not AA.