Just for context, I am the 2nd highest ranked necron player right now, so I have a lot of experience with the faction.
Let's start. Most necron weapons only have a range of 9k which incredibly close and comes with its own set of risks. Being able to operate while being that close to your enemy makes you open to ordinance, ramming and boarding.
Boarding is great against crons ships, because you can only bring a few of them thanks to their high price. Ordnance can be shut down by starpulse, but against good players with torps the necron player can only prefire starpulse. Because of this pulse can be baited out. Ramming is also amazing against necrons because they don't have the Brace stance and they cant regenerate morale with any rally-like abilities. Basically the ideal range for a cron ship to be is between 4500 and 9000. A distance which is both hard to maintain with slow ships and dangerous to be in.
So here we are. Inside 4500 range cron ships will lose to any close range brawl fleet or heavy boarding fleet, and out of 9000 range they will lose to any long range kite fleet. Quite a window, huh? Thanks to all this using the Mass Recall skill is mandatory and the perfect ships to be recalled are two cairns.
The cherry on top in this situation is the fact that necrons are the only faction in the game which have less value in any of their cruiser-size ships than in battleship-size ships. Cron cruisers cost too much for their performance. It’s really hard to make them work in any point-bracket because nothing fits well. Seriously, just think about it. You can go with 2 cairns, LC and escorts, or only with 3 BC, which have less combined firepower than two cairns (only faction who has this ratio actually), and some escorts.
I propose this - buff necron cruiser and battlecruiser or reduce their price along the lines of 15-20%. I would prefer price reduction. It will give more variation in regards to viable fleet compositions. You could also give them <4500 range AP, with or without the former changes, which would make crons a close range threat and would make cairn flagships viable considering scarabs and fire assault upgrade.
But here is the cool way of making necrons smaller ships more viable. Give scarab swarm ability to all cron ships bigger than LC, but make it less effective ofc. I would say like 5 dps per scarab swarm. Because crons don't have torps or carriers it will make them feel unique and more fun to play.