I have had a long day so someone needs to give me a TL;DR version of this. Or a video version if possible.
It seems like you have to completely alter your play style when you are using Mythic Rhythm.
You have to first get the MR buff up by attacking 3 times. Then you have to apply a single EP manually on a target which will be the MR buffed one... THEN you use SSS on that single buffed up EP to spread that buffed EP around with Gungdo Gear explosion from the SSS.
In any case this makes the build have a higher skill cap when it comes to pushing higher GRs.
Yeah, I am not sure what he is saying.
Single Target
U2 will apply MR-buffed EP after the 3rd generator strike.
(If you apply EP manually after the very first 3 hit combo, you will actually be overwriting a MR-EP with a non-MR-EP.)
So if you wanted to make sure you applied a MR-EP to the RG (and don't trust U2), then gain the MR buff and apply EP manually to the RG that has EP already.
When an RG does spawn adds, SSS before U2 so you can spread the active MR-buffed-EP on the RG to the adds instead of non-MR-EPs from U2.
First he is saying that U2 will apply MR-buffed EP after the 3rd gen strike.
-Makes sense, because EP is applied after every 3rd strike thanks to U2 and MR is applied after your 3rd strike.
Than he says MR will be removed and replaced with a non-MR if you try to apply manually after you already gained MR. -Also makes sense.
Then he goes on about if you don't trust U2(?) and that you should apply EP manually to gain the MR buff.
-I don't get this part because of what he said on the first part. Maybe I am missing something. Won't U2 always make sure you get MR buffed EP as long as the target doesn't have any EP?
-Also, how do you in the midst of chaos know how many hits you have done to the target before applying EP manually that is MR-buffed?
Edit: Ok read further and I get why you can't trust U2. If there are several targets around and you apply EP through U2, only one of the targets will be affected by MR, the rest will have non-MR.
It is therefore better to charge your MR buff by doing a couple of hits at a pack and than dash away, find a new pack and apply EP manually to a single target and spread it spread it through with SSS.
Will try this when I get home.