Those ranges of FPS are acceptable, true, but something tells me you haven’t participated in a WB or GvG yet.
Everyone stutters to a crawl at those choke points. I go from a smooth fixed 60fps nearly everywhere down to 5fps in congested WB fights, and more than once (at a dulla fresh after maintenance) experienced a complete freeze for several minutes (how 100+ users squeezed into one boss room on the channel is beyond me). And that is even with changing everything to the lowest possible setting and even trying to manually limit the number of actors present on-screen via user settings.
The fact the title isn’t optimized is just that; a fact. Playing the game normally you may only notice the drops in FPS when a spammer (hilariously) shouts 50x or there are 2-10 proximity bots in-town in /s spamming. That directly relates to why the game cannot handle WB or GvG atm; everything everyone does directly affects your FPS via packets.
tl;dr? Normal game play isn’t an issue and those frames are standard, acceptable, and A-OK. WB and GvG? Get ready to see what everyone actually complains about with FPS issues/optimization.
https://www.google.com/search?q=tree+of+savior+gvg&ie=utf-8&oe=utf-8#q=tree+of+savior+gvg&safe=off&tbm=vid
Click above and view any GvG you want from the list. I assure you not everyone participating has a potato and some are even top-of-the-line PCs. It’s just how ToS handles the net code sadly.