I think we can chalk this more up to other items being ass.
They need to remove AP scaling entirely from items, cuz they've been balancing them around that and thus making those items worse for everyone else ex. Ludens, Ionic Spark and Locket.
Ludens needs to be fixed already, it still deals 100 spell damage.
Seraphs just feels subpar on everyone other than Yasuo, Akali and Lucian and should probably refund like 30% mana rather than a flat 20 (hell you can even make it 50% as long as you don't allow them to stack).
Hush needs to be on every hit, not just a "high chance" cuz the moment the RNG doesn't work and they cast a spell the entire point of the item is moot. It also builds out of Mana + MR making the stats extremely unwanted.
Which brings me to MR needs to be buffed. Any MR item for the purpose of reducing magic damage outside Dragon's Claw just absolutely sucks. Nerf Dragon's Claw if you have to but for the love of god buff MR in general. I'm not saying BT isn't amazing, I'm just saying the MR stat itself is too low to reduce spell damage by any meaningful amount.
Disarm is actually nuts but it builds out of Armor + MR when you typically want this on a backline carry who can apply the effect fast and repeatedly throughout the fight and potentially to multiple targets (Gunslingers).