Actually, I would argue that Syndra is the strongest bot lane mage ATM (Gragas/Diana are the only real competition in terms of how many champions they can combat). And she is not bad top lane, she isn't quite as devastating as Brand, Eve, or Zyra, but she still provides good DPS against clumped up enemies and can erase a problematic melee range low durability champion almost at will. Having Sona's ultimate on a low cooldown is also a very nice bonus.
Muramana sounds nice, but is largely a gimmick. Syndra burns through mana too fast and wants as much power as possible in her non-ultimate spells.