Check the mod priority guide:
https://docs.google.com/spreadsheets/d/1ty239kyJbBs1sLhTo1JvSWuN0mIJsK1nwVdI6OLLtXo/view?rm=minimalOh Lee, my darling Lee, my beloved Lee. Lee-Enfield is my personal favourite doll, I cannot describe how happy I was when her upgrade was revealed, and am very pleased to say it’s a great one at that. Given Lee was already a great base to build from, there was very little chance of this upgrade being bad. It’s pretty generic though, and for the most part she’s just a better version of her original self with some new bells and whistles.
In terms of damage dealing, an non-upgraded Lee still remains a good and safe choice, though one now overshadowed by many of the newer RFs. Lee MOD does aim to improve her raw capabilities quite a bit, with her boosted Damage and Rate of Fire stats, her special AP ammo from MOD3, and the boosts from Skill 2. However, the new main thing going for her is her brand new support capabilities.
First, Lee’s Skill 1 was improved to now give a Damage boost to any doll on her tiles upon activation. Her new Skill 2, Proof of Glory, aims to take her even further by either buffing the entire team’s Damage (if she’s the echelon leader) or buffing her own Rate of Fire (if she isn’t) upon receiving a buff. The maximum amount of stacks depends on the number of allies on her tiles, so it can help to have her tiles occupied, but this may not always be ideal depending on the situation
Both Skill 2 buffs are very effective, and if you equip Lee with her SPEQ-Set, she can grant both effects at once. This greatly increases her flexibility and makes her even stronger, but does not meaningfully change her use cases or priority due to modern RF options and enemy designs..
So overall, Lee MOD gives you an improvement on an already effective base, with additional support capabilities that let her fill a new niche, but comes at a very high cost and does not grant her a true defining speciality, especially with new doll and enemy designs. She is at her best with her SPEQ-Set so that you don’t have to choose between her buffs, but MOD2 and even MOD1 are fine budget options as well.