Desperately need help

Love the game and got to level 100 in no time, but after that it was a continuous struggle to get any further and i am now level 156 and have no clue on how to continue. I have a Grade ten (lvl4) Bone Cannon, but can not beat a lot of the 8 star monsters (like the batelgeuze who is commended level 8, but i am stuck in the quest on chapter 7, as this batelgeuze is unbeatable (just not enough) time, or my grade 10-4 is too weak (30 Wyvern gem shard to get to level 5 , which will take a year, and upgrade from 3 to 4 did not help at all)).

So what to do? Stuck at the quest, all the other weapons are way lower and way weaker than my Bone Cannon (which i do not even enjoy much, but it is the best i have). The fun is really gone totally and after putting a lot of money in the game, i feel like i hit a wall that is apparently to steep for me.
Worse than that; i now believe they are deliberately making the game more hard: (like adding the tundra made a lot of tasks 25% harder) (like adding more monsters making it very hard too find specific monsters, so all these tasks also increased very much in toughness)

Any hints are welcome to get me my love for the game back and hits on how to proceed

Upgrading to 10-5 does nothing if you dont use wyrmstake. Focus on artillery 5 and lockon.

Start farming for elemental builds of your fav weapon. Use the bone lance to farm

@maebelle Thanx for your tips, and i will surely try this.
However, this is exactly what the game lacks: how can i know that upgrading has no use unless you use Wyrnsomething?? How do i know i have to use artillery and lockon (especially since i have a seprate lockon build for the part-assignments)? How to solve the problem of having only one decent weapon and how to upgrade the others without ever using them on monsters (as all monsters are too strong).

Go on discord or Reddit. Read guides and watch videos

I think you should read the in game description of all the skills and decide which skill you need to improve your damage, i think this is a skill and build issue rather than game decide issue. With the current build available, i think with a g9 art5 build can easily beat all 8stars.
You can also ask here, im willing to help.