If you think there?s too much stuff on the table after Turn 3, you most probably fight a shooting game as in the old days of 2nd Edition Epic. Which just might work with an ork list tuned for that purpose (lots of Mek upgrades), unless facing IG.
The way to achieve decisive results in E:A is via supported engagements. The orky way to do this is double moving a Kult of Speed with lots of Skorchas within 15cm (FF range) of a target formation placing a couple of Blast Markers, and then engaging that target with another formation, since you need speed say Stormboyz, Kommandos or an Air Assault with a Landa.
When the dust has settled the target will most likely have lost a lot of units and be broken all the time since it has just lost an engagement.
Another useful tactic is going for a Crossfire, the -1 Armour Save is the great bane of units like Leman Russ tanks, which will take almost twice as many casualities when crossfired (save dropping from 75% chance to 56%). Orks don?t depend on this as much as other races as their AT fire as mostly weak and they have the feared Zzap Brigade, a Big Blitz Brigade with 2xMek Super Zzap Gun upgrade and a couple of Flakwagonz included. The Titan Killer ability on the Zzaps makes a mockery out of all armour, the AT fire form the Guznwagonz is basically just cosmetic. And yes, 4+ Reinforced Armour units like Terminators and Leman Russ are perfectly valid targets for TK(D3) weapons, ith may be overkill, but so what?
Expanding on other armies, Marines are all but useless in a shooting war and you can?t successfully play them in E:A without using Engage/Support, Crossfire and Air Assault.
Gargants are useful as Break their Spirit formations (as your opponent will have difficulties killing them), mobile cover/Line of Sight blockers (War Engines block LOS, and Gargants are big models) and can be used as an assault wedge, if the terrain between your deployment zone and 2 objectives is close to each other (Gargant base width +30cm , so that you can claim/contest both) is clear or at least passable to War Engines (having Walker they don?t need to worry about Ruins too much).
Hope this helps.