Why do people say Seraph's Embrace makes you weak early?

Yeah I get it, It costs 720g to buy , but nobody says anything about how costs 600g. Why are , , and other champs that buy not defined by a "weak early game" like users are?

is fairly cheap now, and together with it builds into an extremely strong item. gives 140 AP on just about any mana using champ by itself when fully stacked, closing in at 160 or even 180 with mana items built. It gives more AP than any other item, and with the recent buff to 's passive it synergizes extremely well. And let's not forget that huge shield, mana regen, and extremely high mana pool increase.

When you initially complete , it gives you 80 AP + over 20 - 40 extra AP from the passive, which is already on par with every single big-ticket AP item in the game. I just don't get it, how does supposedly equate to a weak early game? Honestly I see little reason not to get it on almost any mana using AP champ right now.