I have an FUT scar and yes they can be that bad....mine is pretty wide and is ear to ear in a semi circle shape.....when my hair is grown out normal length for me you can't see it.....plus my hair below the scar is noticeably thinner than above. I have heard several times that the thinner hair below the scar has nothing to do with the strip surgery but it's odd that there is such a difference between the hair above and below the scar. I have seen other strip scars (online) that looked pretty good, but even a good one is gonna be pretty obvious with shorter hair.
I have just had FUE and the scarring is much better.....but there is still scarring....it leaves tiny white dots from where the grafts were removed....they seem more obvious when looking from below up at the scalp, but they are pretty much only obvious if your scalp is shaved....having even a little length covers the fue scars.
As far as yield I can't say since I just had my fue a month ago but the results I have seen online look like the yield is as good as strip.
I will say this, if I had it to do over I would only want fue (only strip was available when I had my strip) and at some point I might have my strip "repaired" with fue grafts and even then I know they can only make it look so good.
I know you feel desperate, but you are only 21 (I had my first surgery at 20 or 21) and there is life after 25, 30, 40 and so on. I always get a kick out of the people who say they wont care when they are 30, if you care now you will care then (although there is no doubt hair loss becomes more normal the older you get). My point in saying that is that you shouldn't rush into doing anything out of desperation.