The thing is i'm looking at not adding harlequins to a eldar force but adding craftworld eldar to a harlequin force which is quite different. For example; in a standard eldar force rangers are terrible as they are static and expensive when compared to guardians. Being equipped with a sniper rifle makes battle focus on them is pointless as they can't keep up with the rest of the eldar force due to the weapon being heavy. However when added to harlequins that can fleet, run & charge all in the same turn with move through cover and can hit and run eldar units won't be able to keep up with the harlequins anyway unless they're doing drive-byes from starweavers. Obviously the best unit to doing drive-byes from starweavers is fire dragons, my problem with this is 2 fold; a.) the starweavers don't have a reliable way to scout, deepstrike, infiltrate or outflank. They don't even have skilled rider which would have helped, they have to charge up the field (using their one use 4++ save on the way) to hopefully pop tanks & transports at the same time as the rest of the harlequins get there without being destroyed in the process. b.) as eldar units can't keep pace with harlequins then i'm looking for a long ranged solution, a static fire base that can open fire from first turn, this unlike in a eldar army brings rangers back as a possibility for the allied troops choice in my opinion. (in case your still thinking wave serpents are the go remember that you can only bring one.. maybe two wave serpents and they are most effective in mass)