Advise on Stone spending for UW

I am currently saving up to get my DW to quantity of 5. I have one extra from a Legendary module effect already. However, I saw a post online discouraging this and now Im wondering where I should put my saved stones going forward.

I am currently at around 30k cells and 1T coins per run, getting to around wave 6k on tier 9. I stopped focusing on econ and started trying to increase damage to get higher in Tournaments. I get between 12-8 in Platinum pretty consistently but cant break into champion.