Dunno... I actually edge out to Loki w/ 2 days prep... but only if he comes into the battle with active effects. Also I don't know if he could block speedforce based attacks like a speedsteal that would just outright stop him. Supposing he could the follow up would be an anti-kinetic energy field around him that just reduces kinetic energy outside himself to nil. A lot of this is dependent on his capability to stop access to the speedforce. Personally I don't think he could as I'm not sure beyond zoom and the flashes that anyone actually can influence the actual speedforce.
pretty much. I give loki an advantage because he has more viable options against the flashes which they pretty much would have to rely on the speedforce speedsteal to completely stop all of Loki's functions. But there is no guarantee for them that Loki wouldn't be able to find a defense and Loki in turn has options like intangibility and outright kinetic energy nullification fields to stop them. Also his magic is not necessarily reliant on catching up to them as IIRC he's got direct effect magics that don't require him to actually tag the flashes.