What a troublesome time you had with those beakies. I'll give you a couple of hints for next time and hopefully Wyddr doesn't skulk around these threads to gleam any orky knowledge.
I've got some experience with ork walkers and I have experienced terrible times against armies with krak and melta grenades. Now the unoffical GW suggestion has been to change the ruling to only one member of the unit can use a grenade in assault, which would have made your dread much more survivable. But, if you guys are sticking to rules as written, then I have some suggestions for you.
When using a dread to assault an infantry unit with lots of armour penetrating grenades or powerfists or other high strength weaponry, the key to beating them is in the multiple assault. Use your boyz to assault the unit first, which will hopefully whittle the unit down slightly, but will most likely engage all of his models with your boyz. read Big Rule Book page 55 under Move Initial Charger With all of his models engaged with your boyz, as a second charge in the same turn or in subsequent turns you bring in your walker. The walker must make it into base contact with one of his other models, but you can choose where. You can stay away from his power fist or reduce the number of grenade attacks against your walker. With his models engaged, he cannot reposition them to focus attacks on your walker, only if he kills the enemy models he is in base contact with and then he is able to engage your walker with his 3" pile-in move, but then he still cannot attack until the subsequent turn. read BRB page 55 Directing Attacks
By doing so, you force him to split his attacks between your units and if you're smart and are able to strategize in advance, you can effectively nullify any dangers to your walker, while your walker can deliver all of its devastating attacks on your opponent.
Some other suggestions would have been to outflank the koptas, keeping them off the board only to spring into action and hopefully get some rear armour shots on his dread. It may have also been useful to throw a buzzsaw on one of the koptas to make it more deadly in close combat. It also looks like you didn't split up your koptas. Please, please, please, if you have the empty slots, take the koptas as single model units. He'll waste time trying to shoot down a single kopta with a whole unit, while you jink and keep the other one safe. There is very little point to keeping them together and if you lose one in a unit, your taking a leadership test. Stick with single ork units at all costs where possible.
Lootas met the fate I predicted. If you're going to take that many in a unit you need to protect them. Otherwise, if you're determined to keep them, split them into two units of 5. It'll at least slow Wyddr down in wiping them off the table. The problem with two units of five, is that you'll lose another heavy slot.
Trukk mobz are fine in my books, but not putting a nob in a unit is not normally a wise idea. Skeeter has always referred to boyz as a nob delivery system.
The nob is what is going to win you combat. Even if you're taking shoota boyz, their primary goal is to get into close combat. Big choppas are great and I love taking them, but don't be afraid to mix in some power klaws. It's great to get a high strength hit on a marine, but with power armour saves, it might be for nothing. I usually put the big choppa on the warboss, as he has a higher base strength and then power klaws for the nobs. Or better yet, give the warboss a killchoppa for some nice insta-death shenanigans.