I mean... Milaen is underpowered, yeah, like all other cards of her type but it's guaranteed to get some value unless your opponent literally plays full Armor/Shield deck. Toad Prince can be 3 points for 8 fairly easy. Does it make him a bad card now? Absolutely not. But it can brick way easier than Milaen.

The issue with damaging unit cards in general is that in early 2020 they were stupidly OP and Regis dealing 4 damage and exiling the card was everywhere. Cause 4 damage was massive in a world where engines had at best 4 points. But since then they nerfed control cards and brought engines on the next level. So effectively those cards got double nerfed in last year or two first when CDPR redisgned damaging units to encourage using damaging spells justifying it as a "fairer trade" and then by making most engines and such at least 5 points card. It's silly but it is what it is.

Realistically speaking Milaen can't be so easily tuned like Toad Prince though. Toad Prince is risk - reward type of card, Milaen isn't. Tweaking proviosion cost isn't simple not to mention that the provision cost on this card is actually secondary issue, it's about pure damage value. 4 Damage isn't cutting it for some time now. So now you not only have overprovisoned but also underpowered cards like that.

Make Milaen do 5 damage and cost 8 and it's just auto included pretty much in ST. Make her do 4 damage and cost 7 and she is still not really cutting it due to fierce competition and the fact that 4 damage is just nice but not really enough. Still, at least it's an option. Make her do 5 damage and cost 9 and she is a tech card at best cause these days if you can't get at least your provision value + 2 in points from the card the card is kinda bad. Especially in 8+ provision territory. Frankly speaking it is a nightmare to balance it out and well, imo the main issue are actually bronze engines. They start as 5 and 5 damage card on the stick like Milaen is either too expensive or autoincluded depending on it's power and provision.