You're probably running shitty masteries and runes then. I pretty much never need to buy armor or mr until one lane or role starts to show dominance, cause my base armor and mr are at least 40 or so at level 1, and will hit 80 or so by 6. That's already hitting the curve for where extra armor and mr starts to cause less and less damage reduction.
And Syndra still has only a 40% win rate. One of the lowest in the league, alongside Karma and Yi in ranked games.
It's not the fact that she's difficult, cause she really isn't. It's the fact that everything she does, other champs will do better. Single target burst is matched or improved by champions like Akali, Diana, LeBlanc, and Kassadin. AoE slows and stuns are matched or improved by Kennen, Morgana, Cass, Zyra, and Anivia. Utility is matched or improved by Orianna, and Lulu.
All for much less effort as well. The amount of effort you need to put in to double the damage of your ult takes too long and is too intensive to use during teamfights. At most, you'll get 2 extra balls out, so it will hit for around 1400 or something before reductions at 16. Not shabby, but it's still a lot of work for it, considering it also has a range shorter than all of your spells. She's more a fun champ to play than a viable champ. Because no other champ allows you to say you smacked them silly with your balls.