The avatar is one of the better fortune targets out there. I do play against crons alot so a lot of the attacks they shoot him with are not low ap so his 3+ is what is getting the reroll. In a foot list with a sword wielding wraithknight jumping/running 6 up the board(18" in their face each turn) he will have other threats to take pressure off him.
The list should have enough threats that need to be shot at, the scorpiens are pretty self sufficient as they are survivable until needed. I would still go defenders for guardiens as if they urd have better shooting than the charge anyways(leave the assault to the aspects). There is another threat in the spears zooming up to the back into cover and jinking if need be, their focus will be getting rid of vehicles. Banshees will need to be protected, they will stay back as they got the speed to move up faster than the rest as needed and act as cleanup instead of the first wave.
Here is the plan with the eldar warhost
The defender guardian battlehost(would have to prob focus more on the guardiens so less focus on extras)
Cc aspect host(5 spears, 10 scorpiens, 6 banshees)
Thinking another shooty aspect host(with spiders, avengers and reapers) or going full dire avenger shrine
Wave 1 - The knight, spears and scorpiens would be up close t1 due to speed/infiltrate
Wave 2 - the avatar backed up by the dire avengers/some guardians(not all) and the heavy support weapon will either move up with them or fire if needed. I would consider the Farseer in the back of this wave buffing the avatar hopefully with fortune, if not that doing other runes of fate powers. The spiders if picked would come in wave 2 dealing with things that are pressing threats.
Wave 3 - more guardiens and this would be where the war walkers, vipers, banshees and reapers(if picked) would go.
Fritz always talks about the wave type lists and this by no means is the only way to go but it gives you a nice strategy to play with. I would prob use the d-cannons for platforms and the wraithknight has a d sword but I doubt anyone would call this army cheesy.
The knight would be a decent magnet that if not dealt with first will decimate the opponents back lines, but if he does go down trust those points went into saving your mostly weak foot army from being picked apart. That's what the first wave does best is to provide 3 shoot me now targets that are close enough to them that if not dealt with are an issue.
The second wave is there to follow up the first and quickly, the avatar will be as much of a target as the first wave stuff so would have to try and keep him safe unles fortune goes up and if it does he can take a beating. The supporting guardiens/dire avengers should shred some infantry. Those d-cannons will be another fire magnet, it's there to keep the weak troops safe from close up threats. They have to be protected from assault but the avatar and troops will bubble wrap them quite well.
3rd wave will be the fire support and objective campers any guardians here will be helping plink vehicles with a Brightlance or eml, and staying near the war walkers/vipers keeping them with prefered enemy.
This is my theory hammer for my ideal avatar list, it's definitly an army that would not have a huge amount of models left at the end of games but it still has the ability to win and in a way that would be insanely fun to play and play against.