A diamond MF otp here, I want to give you some feedback about the MF nerf.
Her nerf on PBE currently states:
Double Up (Q) - [removed - "If the first shot kills its target, the second deals 50% increased damage."]"
So first of all, you need to think about the fact that MF is not an overloaded champion. However you're removing one of her most fun and rewarding mechanics, which makes the champion a lot less fun to play and also removes one of her mastering skills. This makes the champion a lot more dull and also gives way less options to do in the early game. In other words, it completely destroys her laning phase early while also making it pretty boring. Is this really the way you want to go?
Second, the empowered Q had a lot of counterplay. Yeah, there are people who accidently take it because they forgot about it, but most of them adjust immediately to it and avoid the empowered Q. People should be punished for not playing around a mechanic. By removing this, you're basically removing a lot of MF's pressure and generally making it a LOT easier for the enemy to just do whatever.
Third, lethality is already getting nerfed and MF is VERY reliant on lethality so any nerfs to it will hit her pretty hard. Let's go back a few patches, in 7.1 where armor penetration was reworked into lethality, lethality was pretty weak and so was MF. I thought she was in a fine state but was still getting outclassed by other ADC's. However when you buffed lethality into a really strong state, she became top tier. Guess why? She's extremely reliant on lethality. So waiting a bit after the lethality nerfs hit would make most sense before nerfing a champion like MF. Nothing frustates me more than a champion getting nerfed while at the same time his/her core items are getting nerfed too. You need to have some patience.
Fourth, even after she's still too strong after lethality nerfs, you should not directly remove a rewarding and fun mechanic (I said this before). I'd suggest you look at her passive. It currently encourages her to switch between targets as an ADC. You basically get punished for AA'ing the same target twice (as an ADC, this makes no sense). Her current abilities (passive, Q and R) are all pretty reliant on lethality, by removing the mechanic on Q it won't make it any better. I'd suggest changing the passive instead since the Q is reliant on her passive and make the passive more meanful for actual autoattacking. If otherwise you think her as a caster ADC, then don't change the passive and don't remove any mechanic at all. Because she is currently receiving enough nerfs from the lethality nerfs.
So in short: be patient first, wait for lethality nerfs to make any effect, then judge the champion's balance state and then (don't remove a mechanic...) act on her problem.
That was my feedback, I really hope you read and listen to it. It would mean a lot to me.