I voted YABU because I think your DS2 isn't to blame for his behavior at this age. However, I have empathy for your situation, and can only imagine how difficult that would be to navigate.
Some children have vastly different levels of chill, and need different parenting tactics. My own DC2 is the calmest child. Whereas DC1 is a whirlwind of a human being. I don't think of DC2 as proof I'm a good parent and DC1 is the outlier, because I try to meet them both where they're at.
E.g. DC1 needs hugely limited screen time and sugar to stay semi calm. The behavioural impacts of a freddo and 20min cartoon ricochet through our whole day. They need to quite literally run off their energy, and be given a lot of opportunities for rough and tumble play. Often children who hit have high sensory input needs.
I give choices - you can't hit your sibling but you can hit this pillow. You can't kick me but you can kick this ball. You can't bite anyone, but you can bite this apple. Gives an avenue for the behaviour and teaches them appropriate ways to funnel fheir impulses.
I repeat these as often as I need too, as calmly as I can. The bigger your reaction, the more they'll repeat the negative behavior. Look up Janet Lansbury - brilliant resources.
I also speak in short sentences when they're melting down. They can't take in too much, and can't split their focus at that age. If I need them to listen to me, I make sure I have their full attention first - making a high pitched beeping noise works. 😅 I get on their level and make full eye contact.
I try get curious before I'm furious, and enquire as to why they behaved that way first. Often times they can't tell you - so if I'm calm enough I'd say something like "I think you hit your sibling because you felt angry they took your toy". This helps them recognize and name their emotions.
I do a lot of work on emotional recognition and regulation - read stories on feelings, name what I'm feeling, name what they might be feeling or characters on TV, etc., when they can communicate it cuts down meltdowns and bad behaviours.
Co-regulation is also still key at this age. If I'm too triggered to coregulate with them immediately, I have a little script I follow "I need to take a deep breath to calm down. Mummy loves you. Mummy will come back".
I personally don't find time outs work, but I do use clear consequences after warnings.
... And even given all that I still lose my cool sometimes and just yell or say the wrong thing because DC1 in particular really pushes my buttons. If that happens, I model what to do in terms of saying I'm sorry, that it's not ok to yell, and teach them how to repair.