My 5 cents, technically speaking being f2p doesn't include the pack code or the 99 expansions that give you access to a lot of adventures.
Having an these adventures it indeed allows you to play the game just at normal and progress enough to reach the epics.
Not having these extra content, you will soon reach a point that there are not enough quests to level up and you will need to repeat stuff.
Point two, the game has three conceptual parts.
Heroic
Epic
Legendary
For heroic, you can play in normal with a bad build and still enjoy the game. You can literally for many quests just buy a hire and let the hire, pets, summons to clear the dungeon for you.
The moment you goto epic, it is like a different difficulty scale. The same happens once more for legendary.
On top of these difficulties come reaper as yet another step to spice things. Which has its own scaling.
When you are aware of these, and when you are aware of your limitations you can choose the difficulty that works best for you at each game stage.
For example, I solo run heroic r3, epic r1, legendary elite with my main toon (5pls). Because this is what I enjoy. I can run leg r1 but it takes to much time for my taste, without actually increasing the adrenaline.
I often play alts, currently I'm actively playing 3 characters on Moonsea, and 1 on each other server. Each character plays with a different static group.
Only one is a "viable" reaper build and can go fast (zergish if needed). The rest are for elite and to go slowly.
The trick in enjoying, is to have a good static group. I play with my friends, I help them improve their characters so that we all contribute in the dungeons. We are 3-4 people at each run, so together doing elite is easy.
I also play with a Perma Death group, and even if we could easily zerg we don't! We go slowly carefully and have a blast. Last time was the first I almost died. And yes it was a trap I missed

. And believe it or not that was fun! I remembered the adrenaline of actually playing RPG where death means something.
I am also introducing my nephews to the game. We played a lot of normal in the beginning. But being 3 in the dungeon it made us very easy on Normal even for my nephews. Elite and reaper was sometimes deadly for them. But I did "pushed" them a bit to finish on elite a few coin Lords quests do we get the extra inventory.
I don't regret it, but I think they would have enjoyed more playing on hard.
TLDR?
the point is, the game gives you a lot of options when you have content. And there are players in the servers that play in many different ways.
Experiment, play with others and find what you enjoy! More importantly find a group you enjoy playing with.