I know I had said it ... But since they didn't say anything, I ask again:
For Modders / Admins / Developers of the Arknights mod:
Is there any news regarding the mod?
Why did you remove the old system?
Are you going to update it?
Are you at least going to remove the "No DP Cost" option, which is a feature that is a guaranteed ban??
Will you give any explanation, if you are working or are you going to work on this mod?
...
Could you at least answer me? 
Rather,
to all of us.
Thanks.
Not Strictly a modder, but the old system has flaws and are easier to be detected by anti-cheats. What I heard about (one feature of ) the Anti-Cheat system is that they took records of your operator's stats, maybe at the start of the battle/Mid-battle/the end of the battle (or just totally random) and store them for comparison, which means that changing the Def/Atk of the operator will be easily detected.
From my observation, currently how change operator atk works (for ranged unit/archer) is that they multiply the projectile of the archer mid-air by your selected rate, so that the atk/def of a operator stays the same.
This do post some issue, since all the projectiles are multiplied, not only yours, but your enemies and even the stationary crossbow turrets.
The above statement can be proved if you have Texas (5-Star Vangurad), her 2nd Skill rain projectiles from the sky, she's one of the few melee operators who'll be affected by this multiplier.
Why doesn't it work on some skills/melee op/casters? My guess is: Based on the Unity engine, sniper operators (as well as Texas' 2nd skill, mentioned above) launch a projectile, whether it's visible or not, to hit and do damage to your enemy, it has a travel time mid-air, so the ATK-multiplier can multiply this projectile, however, most caster/melee attacks does not have a travel time, they hit immediately, and there's no projectiles involved, as a result, they can't be affected by the current ATK tweaker.
However, since it does not mess with the base statistics of your operator, it can safely (almost?) bypass the Anti-cheat system.
That's why they removed the old ATK/DEF tweak function. Hope this helps.
TL
R, anti cheat detect abnormal statistics of your operator (ATK/DEF wise), new ATK boost feature multiply projectile to bypass detection.
