In addition to all the points already stated: step up your offensive game. Several of those characters don’t have the greatest reversals for a reason, they are meant to pressure pressure pressure. Look at it thusly, you aren’t loosing to mix ups and the like you are loosing by relinquishing momentum and control of the match.
Online you will encounter several types of players:
The genuinely good, who will likely bulldoze you. These are the guys that on your first match you think you do relatively well, then you get your ass handed to you. They respected you at first in order to download your patterns, feel you out to see what they are working with.
Then you have players with an effective pattern but lack the ability to adapt. If you can’t beat these guys YOU are the scrub. Lag can make it difficult but over time you will get to the point where you will bulldoze these despicable dipshits. Beware though, a genuinely good player can appear no different if the gap in skill between the two of you is great enough. The difference being, a good player will modify his gameplan if you can counter it, the other guys will keep with it or resort to randomness or poorly thought out “strategies”. There is some possibility of training these guys to react how you want but most will be you figuring out their pattern and make with the pressure, predicting, and punishing.
The dyed in the wool scrub is the last but easiest to deal with. These types are random or a few steps above with one or two answers that they try to apply to every situation. Modify your approach depending on the match up. You won’t be able to teach them ANYTHING. If they lack a strong reversal PRESSURE them to death, if they have one and are relying on it, bait it and destroy them.