Don't you remind me of that game! Back when I used to play it you'd bring your weapon to around tier 12 and your gear to at least 8 or 10... you'd literally waste at least 1000$ just to get your stuff pimped to where it was remotely useful.... until the next dungeon was released at which point your gear became pretty much…
Collect AD and buy the purple <font color="orange">HAMSTER</font> from the AH. That's all there is to it. No need to even set foot in any of the dungeons ever.
Everything in this game is set up towards persuading you to hand over your wallet. Either grind for months and months or shell out the dough and have it now.
Fusing success chance for tier 5+ is insanely low and you basically need some mandatory additional "help" which you have to pay for to get a guaranteed upgrade. Unless you want to waste literally 100s of runes trying to upgrade them.