But Somerset wouldn't grow by 50,000 people. Somerset would be the same, the Unified Local Government of Somerset/Pulaski county would govern an area of 63,000 people, that's it.The reason Elizabethtowns only a class 4 city is because thats what they wanted it to be and asked the legislature to be (from my understanding). So they can be rewarded with more money to finance their city due to the increased tax they can charge. Your point about Burnside basically proves what I am saying. Burnside asked for their class and they got it.
And if Somerset did grow by 50 thousand people I am fairly certain the legislature would at the very least let us be class 2 if we asked to do so.
The legislature doesn't just make anyone whatever class city they ask. You're probably right about Elizabethtown, as they would be at least a class 3 if not a class 2, but Junction City fought for years to go from a class 5 to a class 4 after having been turned down before and they have 4x as many people as Burnside.