We know. We saw it the first time... time after time, after time.
And we also saw improvements along the way. Not enough by a country mile, but he has shown steady improvement.
Several of your selected plays showed Costa being beaten badly, some of them showed blitzes with Costa engaged with his man and a LB or stunt going up the middle, Costa is responsible for one guy, and that guy is a 3-4 NT type often enough- why he is one on one with him is beyond me- I wish other teams would be considerate enough to leave Rat one on one.
Smith and Free will swap sides, the other three spots are up for grabs. Not sure why Costa, the youngest and least experienced of the bunch, and the one we could expect to struggle the most, gets singled out I don't know. Many of your selected plays, Costa was just one of the guys getting beaten,
This o-line is still the number one weakness, and serves as an anchor to hold the entire offense back. I say average at best, others like to say "mediocre" at best- neither is nearly good enough. I hope next season we can honestly say the o-line is better than average, or even good by NFL standards.