The weld ending before the end of the plate lets it tear a lot more easily when things flex (and then break dramatically). I discovered this when I first started welding and I was testing my welds... basically I'd weld some plate, clamp it down and wail on it with a sledge hammer to see what happened. As time passed I discovered I could fold plate over with a decent weld as long as it was complete across the entire plate. I'd occasionally see tearing on the outside of the weld where the weld didn't go to the very end of the plate I was welding.
Also, in my experience welding is about 80% metal prep, the better beveled the pieces are and the cleaner the metal is the better the weld. It doesn't look like you cleaned the metal very well, and I would suspect that's probably why the welds appear to be a bit porous. The bracing to the frame support looks like a really dirty weld. If was to guess it almost looks like the metal was painted and then welded.
From some of those side shots where the top plate is sitting on the frame rail it really does look like the plate on the frame rails is a smidge more than .125. If that's the case "eek".
Honestly, coming from an amateur with a bit of experience that has gotten a tremendous amount of advice on here and elsewhere that has proved to be good. Assuming the plate you're using is at least 3/16", I'd weld in a plate from your side pieces to tie them together and I'd weld it to the frame rail cross tube. I'd also weld in a plate from the bottom square tube at the bottom/front of your winch plate up to the front edge of the fairlead. I would also seriously consider some kind of plate towards the rear of the winch plate to act as a rib.
Basically you'd be making a bunch of triangles and adding a rib to the back edge of the winch plate which will help keep things from moving around. The square tubing you have on the outside of the front winch bolts that's on the underside of the winch plate is basically doing nothing. Your fairlead mount in it's current position is just a huge lever on the plate it's bolted to. The first time you're really stuck and pull up or down it's likely a done deal.
There's a learning curve to this stuff. You really don't know till you do it and get advice or see repeated failures. There's a lot wrong with your current setup. It may be fine for a few pulls, or maybe forever depending on what you do. But if you get really stuck I can see things going seriously wrong, and with the forces involved it could be really really bad. A winch plate bumper tearing apart has the potential to be a lot more disastrous than a winch line breaking with a clevis... and the winch line and clevis has been known to tear through sheetmetal and bodies as a projectile.
My advice is free, and you should take it with that in mind. But I'd like to see you be safe and succeed. I'd fix your fracked up shit.
. Ive been driveing the ol lady's jeep for the time being