What determines the marked difficulty level

No it's not. You should also put points into the secondary skill tree at least to the point you get a good consumer ability.

The reason this is better is because most builder abilities are building up point for both weapons you wield. This way you will be able to double the output of consumer abilities and this will increase your damage (or heal) output at least by 15%.

• builder ability: Abilities that build up points for your weapon (up to a maximum of 5).
• consumer ability: Abilities that spend these points and usual do more damage/heal than builder abilities.

Other source:

Why do I need two weapons? What's wrong with just one?

The game is balanced around the type of damage output you can do with one builder ability to create 5 resources for two different weapons, followed by using consumer abilities from each weapon back-to-back, and then repeating this general process. If you have only one weapon, then you have only one build cycle followed by one consumer, and you are essentially putting out only 60-70% of the total DPS that you could do if you were using two weapons.

So don't try to skill up only one weapon to "max" Skill 10 ASAP, because you're seriously gimping yourself by doing so. Right from the start, as soon as you roll into the Sheriff's office in Kingsmouth for the first time, you will receive your choice of a second weapon, and you should always roll with two weapons at all times. Three of your active abilities in any 7/7 build should always be: A) some type of builder that will build for both weapons with each hit, B) A hard-hitting consumer for Weapon 1, and C) a hard-hitting consumer for Weapon 2.

Source: http://yokaiblog.wikidot.com/guides:tswfaq

You need to look at the dot to the left of the name - the color of that will indicate how safe it is. White is and even match, blues and greens will probably be pretty easy, orange and yellow are going to be tough, and red means "Run away!".

The TYPE of dot indicates linking behavior (a single dot is normal, three dots indicate monsters that move in crowds, skulls and crowns indicate lieutenant or rare type monsters).

The color of the name indicates how aggressive the monster is.