I have not fallen into the “themepark trap”, whatever that really means. And I have bad news for you; Tree of Savior is already a themepark game of sorts.
“Themepark” design is so called because you are ushered through the world along a pre-ordained track meant to allow players to view all the ‘attractions’ in an efficient way, much like in an amusement park. Back in 2004 “themepark” design was a revelation that made World of Warcraft accessible enough to become the biggest MMORPG in the world. In the intervening decade, it has become a naughty word because savvy gamers with much more exposure to the genre have picked up on certain common patterns that repeat over and over in themepark type quest design, and it has become a bit fatiguing and stale to see in game after game. This is a totally fair indictment of “Themepark” games.
However, “Themepark” does not mean “game has quests”. Themepark means linear. ToS is a profoundly linear game in its current state, at least in the levels I saw during this beta. Everyone starts in the same zone, progressing through the same zones in the same order. The zones themselves are not expansive and vast, but are a network of narrow canyons, roads, and clearings that have a clear entrance and exit. The negative picture that you paint of “chugging along the railroad tracks” applies very directly to ToS, coal shoveling and all. The Oldschool games which you claim inspired ToS were very, very different in this regard.
I’m not arguing for ToS to be a traditional themepark game (and “themepark” vs “grind” is a totally false dichotomy). I don’t think IMC wants this either, which is why they cannily decided that it would be better to make most of the (many) quests they designed for the game be hidden and require exploration to seek out. This is a smart move! They can preserve the beneficial aspects of themepark quest design–clarity of purpose for the player, frequently visiting new activities and locations, while excising the worst aspects of themepark design-- finding an obvious “quest hub” that overwhelms you with objectives that feel like a list of chores, and the general feeling of being led around by the nose.
You can have lots of quests, and make them rewarding, without turning the game into a “Wow-killer generic brand themepark”. You do this by looking more to games like Skyrim or The Witcher 3. These games are bursting at the seams with quests, but they are still deeply open and sandboxy. You have to find quests and dungeons on your own by striking off into the uncharted corners of your map, experiencing the joy of exploration and discovery, and it’s worth your time if slaying bandits for 4 hours straight doesn’t sound like your cup of tea.
Quests are not evil. These are not the embryonic early days of MMORPGs, and players have a reasonable expectation to be able to progress through the game world and see new things at a pace that keeps the game engaging. Letting players avoid grind via questing does not turn the game into World of Warcraft. Letting players progress via questing does not prevent other players from grinding if they wish to. The bandits are still there, waiting eagerly for you.