You don’t “need” anything in functionally all games unless your end goal is to be the best in the world in which case I hope you have tens of thousands to spend.

Yeah, there’s objectively better units or weapons, usually released with each banner, but here’s the thing... they only stay best for so long. 99/100 the Dev will powercreep (if you’re unfamiliar with the term it’s where the average strength of units increases over time with each release) any given unit within a shockingly small amount of time.

Some games are better at not doing this than others, some make powercreep a core fucking concept to the games design. Point is you’re not spending money to get the best units. You’re spending to get the best units for now. Sometimes less than a month later your shiny new unit will be defuct, countered or just straight up outclasses by someone new and you might be tempted to start this whole bullshit again.

Settle for what you have, take the lucky rolls when they come but don’t try and always get every unit in an attempt to keep ontop of the meta at all times. It will financially ruin you.