That's because they hit AD itemization this patch, and really, there's no better time to do that, then during the highly tentative preaseason.
A lot of the other preseasons focused a lot more on improving the quality of life for other classes like support and jungle, roles that themselves are highly contained. If a jungle item gets out of control, we reign it in and make it something only junglers really care about, if a support item is too strong we increase the active cooldown or cut down on the stats.
In this case however, AD items were tackled, something that's needed to happen for awhile honestly due to how pitiful their items were comparative to the variety of choice that AP had. Problem is, that more than just marksmen are affected by these changes, and the AD itemization pool finds itself largely affecting AD assassins, bruisers, fighters, and to a far lesser extent Juggernauts. Anyone who uses autoattacks as a vital portion of their damage rotation has the ability to opt into these new items, and the flare given to them in order to make meaningful itemization decisions only improves upon that idea of seeing what sticks with all these new toys to play with.
Combine that with the attempt to make masteries more impactful and you have a recipe for chaos. The balance issues are more robust this season because the number of affected champions is far higher, and the changes to make masteries impactful requires that they be strong enough to have an impact, something that's proving to be a bit of an issue, but one they're trying to address.
It'll take a while for the game to get back to a neutral state, there's a lot that needs to be cleaned up, but preseason is the only real time you can drop dramatic changes like this while still being able to do damage control (Since we're inbetween ranked seasons). Basically, be patient. Its going to take time for the game to come back to where Riot wants it to be this season, and most of these dramatic inbalances will likely be handled in a patch or two. (Patches are on 2 week cycles).
The other nice thing about these changes is that its a chance to highlight certain problem champions who've largely been neglected for quite a time. Champions like Jax and Irelia tend to have massive powerspikes when items are changed, and there are a number of champions whose balance is far too item-dependent. Bringing these guys into center-stage gives riot a chance to think about how their power fluctuates, and potentially take steps to bring them into a more centered state, so that they aren't perceived as bad when off-meta, and aren't ungodly abominations when the items align. Balance is a tricky bastard, its incredibly elusive, and the only thing you can really hope for with a roster as big as league has, is to bring the game to center-state. That takes time, for both the developers and the players learning how to fight around the new changes, and figure out what truely is or isn't in a proper state of disrepair.
twisted fate, listed as champion 4(idk how their numbering works but if it is by make order...) is still competitively viable, but his damage is so low combined with an opportunistic high risk, low reward playstyle that he can't compete with other mages or assassins
