Aren't you benching close to like, 400lbs or something? Your triceps and thus your arms should be massive at this point, simply from stabilization. What size did you start at?
Biceps wise, GVT has always worked for me, but I'm a little dude and I rarely do pure bicep or "arm" exercises, simply because I generally get enough from compounds. That and I put on muscle mass fairly quickly if I'm focusing on size, which is not something I've been doing in the last couple of years.
How are you measuring your arms? Did you shrink a ton from when you posted the heavyLyrical pic a year or so ago? Your arms looked like, skin/flesh included, 18"+ already. You didn't look like a bro lifter, but you mentioned you don't do heavy squats/deadlifts so I would imagine with your time in the gym you're hitting the shit out of your upper body. Also, what's your rep/set rotation and exercise routine look like?
Genuinely curious, because from the outside I would have imagined you were clearly over those numbers by now. I know you said they lagged behind, but that seems like a lot compared to the numbers you've posted.