How to buff Syndra:
I have over 1 million mastery points on Syndra, 96.6% of my games in season 7 were played as Syndra and I probably wouldn't be playing League if she wasn't in the game. I'm a huge Syndra main and I've seen alot of people talking about how Syndra isn't viable anymore and while I do agree that she's in a pretty bad spot, people are overreacting a bit.
All she needs are small buffs and QoL changes, bug fixes are even on their way next patch (though every time Riot ''fixed'' some of Syndra's bugs, more bugs were added in the end)
Syndra doesn't need a rework of any sort
_Syndra only offers damage, her pure focus is to deal magic damage and burst someone. So when she's underperforming like she currently is, it's clear to what kind of changes she needs _(bug fixes definitely included since some of her bugs cut her entire damage combo in half and makes entire abilities use mana with no effect)
She's just overnerfed from last season and has very little synergy with the rune system (Riot mentioned adding more keystones so hopefully something viable for Syndra) Reverting some of these nerfs along with bug fixes are more than enough to make her more viable.
Q- Increase AP ratio from 65% to 75% Dark Sphere is her bread and butter, she uses it for every other spell. The fact that the mana cost is this high for an ability you have to use in order to use other abilities with only a 65% AP ratio is underwhelming to say the least. This is basicly a revert from a nerf she got last season.
W- Reduce max-rank mana cost from 100 to 80 (maybe scale down earlier ranks aswell) Force of Will is extremely easy to dodge since it has a long travel time and the same small hitbox of your Q. Having such a skillshot that is this easy to dodge have the same mana cost as an ultimate is absurd.
That's it. These small buffs combined with bug fixes that are thankfully on their way are all things Syndra needs in my opinion. She doesn't need a rework, she's completely fine kit-wise and what type of role she plays.