Lvl difference between player and npc is roughly 10-20% dmg per lvl. That adds up. All solo areas should have a focus of 1-2 shotting the mobs regardless of class.
A yul can easily farm 2-3 spots of white mobs purely on their damage alone after 110. An iss's debuffs are "needed" for dailies and raids.
What you don't understand is you miss so many events to upgrade dmg and atk element. Artifacts, agathions, LA vie, the list is never ending.
The game is now focused on 110+ content. A new player would be wise to understand the current game at 110+, which is typically a solo/duo setup as dd/iss. I would also highly recommend trying to find a clan/friends as that makes things alot easier when the gear is lacking.
Like I said before, if you are enjoying your experience, keep doing you. But, you mention min-maxing. If you intend on getting into the true aspects of L2 (siege, oly, pvp, raids, etc) and min-maxing a char to do some crazy things, you should start focusing on those goals earlier than later and focus upgrades accordingly. There are helpful high lvl players out there, just may be hard to connect with them for tips.