Sometimes I wonder if people actually read when "reading" a manga chapter.
How come Falco can control his titan so well when he just got it?
First, assuming he can just because he is flying is foolish. Second, Berthold was able to use his titan perfectly as well when he first got it. So it shouldn't come off as a surprise if Falco can do it as well.
How come their killing these past nine titans so easily?
First, they aren't. They are handling them much better if it were a titan shifter. But ask yourself why? Well obviously because these aren't titan shifters and just the past nine titans of old. Outside of the fancy abilities they have, they are essentially as brain dead as regular titans. Strong but lack experience and intellect to counter their opponents (the main characters).
You can't expect every aspect to be told to the reader upfront like "We are killing these titans with some ease because without a shifter, they are no different from a regular titan!" A character in story can say this, but if this is the only way you can gleam this information suggests the desire to be spoon fed even the most basic of things.
Now will the main characters win, maybe. The author has always pointed out that, no matter how strong the titan is, if you sever the nape, it will go down. The only question is if the main characters can accomplish this.