actually, if you hard focus on a build from floor 1 (my personal fav is super poison combos) it's less hard from there. luck rings and anything to do with luck on floors 1-5 is a life saver.
You can focus on a build all you want but if you don't get lucky enough to get the items you need for the build, you're left being really weakened and have zero chance of getting to endless mode. Relying on getting luck rings still requires luck to even get them in the first place.
Also even the floor arrangements require luck, because the first floor could have more or less stuff on it, giving you an easier or harder time right away. A run where you get 3 locked rooms and no keys on the first floor is pretty bad. A run where you get 3 heart locations on the first floor but no shops to sell anything means you're missing out on probably 2 of those heart locations because you won't have enough money to afford them.
I get the game is supposed to have RNG, but I just think it would be nicer if we could strategically counter it in some ways. When a game ends up devolving into dice rolls, I lose all interest. If I feel I have no agency, I lose all interest. The more smart choices I can make, the more rewarding it feels.
I think they need to tweak the RNG algorithms to be a bit more conditional for more consistent quality play throughs. For example, if you're going to have multiple locked rooms on a floor, there should be equivalent keys attainable somewhere on the floor. If on the first floor there's 3 locked rooms but I can't get keys anywhere, that's bad game design.