You’re still relatively new to golf it appears. I had a similar problem for awhile. Using a 7-iron was the same as using a 4-iron for me. Problem was that i had developed bad habits that needed to be ironed out by a professional (pun intended).
Club pros are trained to pick out the smallest of swing deficiencies. I highly encourage you to get a few lessons. If not, your bad habits may get worse and become more engrained in your subconscious, making them harder to get rid of.
Looking at your swing, your tempo seems okay. Tempos can change as we evolve as golfers. Whatever the case is use the 3:1 ratio. For example If your back swing is 1 second, it should take you .33 seconds to strike the ball from the end of your backswing.
To me it looks like you have the standard slice swing (i.e. outside to in). Thats pretty normal, but it also reduces ball carry and overall distance in addition to being right of the fairway. Theres a few ways to mitigate this. Position your front foot closer to the ball and/or change the angle of the backswing. For you it appears to be too steep, thus inducing those slices.
I agree, swing with your core. How ever i don’t necessarily agree with other posters that using too much arms is the problem here. Everything, arms, hips shoulders legs, etc need to be in line to square up at impact. If arms are out in front you will normally hit a hook or if behind, you will hit a slice (all other things staying the same of course). Too me, if you’re using too much “arm” then you are leading with the arms and hands. Your arms appear to be lagging behind the rest of you though.
We need to see a video of you swinging with irons. Are you swinging too fast/slow, hitting the ball fat, or otherwise are you simply not letting the club do its work? Attached is a chart of iron distances with various swing speeds to help give you an idea. You could figure out your swing speeds by visiting a golf store such as Roger Dunn, Golf Galaxy, etc and having them analyze you for free.
Good luck. You’ll grow into those irons, it just takes time. Trust us.