To answer Ugglefar: As you said, at this point I think the only possible solution for my playing group is by homebrewing, which I hoped until last I didn't need to, but there are too many things me and my group dislike to just ignore them. Maybe it would be simpler to just use the old system, which I already partly revised.
To answer Jacob: I appreciate you took the time to answer my concerns, but I still believe that the design principles were just too simplistic (even more than the subclasses in the PHB) for our kind of group, which is composed by veteran of RPGs and have played 5e edition since the beginning. Many classes/approaches just don't feel exciting to play for us because they don't have enough interesting features. For example, the 17th capstone of the Tattoo Fighter approach, which should be the culmination of it, is that the extra damage bonus die per attack increases from 1d10 to 1d12, which is mathematically equal to a +4 damage if I hit with ALL my attacks. This is simple unacceptable for us on so many levels, and I don't think I need to explain too much why. To give an alternative, a capstone that would feel at least worthy could be that you can activate your tattoo to act as repellent against magic and give you advantage on saving throws for 1 minute at the cost of 3 corruptions (once per long rest if you wanna limit it further). This is an unique feature that feel powerful, is simple and give you an interesting option. Not a boring, unconditional increase to damage.
So even if it breaks my heart to say this, but the Symbaroum 5e rules for me and my group is unusable as it stands currently, and while certainly other groups that focus less on mechanics could still play it and have fun, that is mostly because for their priorities they could play with any system and have fun regardless.