If you are countering jetbike Eldar list. The better chance is to alpha strike them. I.e. Droppod should be better for your Marines.
Heavy bolter Devastors are bad against Scatbikes, the Scatter Laser also has 36 inch range. So they can conveniently shoot at those
Dev Squads then use their assault move out of rangeq of the Heavy Bolters.
Telion do not need to be attached to a Squad to grant his "rending" warlord trait. He just need to be within 12inch of the unit. A better use of him might be infiltrate him with a Squad of Sniper Scouts, then one to two other Scout Squads (preferably 10men size) with Bolters, then Scout move them into Rapid fire range and you nowhave alarge amount of rending shots. Or you can put him and his "students" near a unit of Thurnder Fire Cannons, you may get four rending, Ignore cover Blast at 60inch range

which I think is awesome.