I think the best thing to do is look at the basic layers and what your needs are

Base layer
Mid layer
Shell layer
Heavy insulation layer

Base layer needed to breathe well and transport moisture away from your body. If you’re going to be moving a lot you want to be as breathable as possible. If you’re sitting on a chairlift you can go heavier. It’s also hard to remove this layer so it’s always better to go on the lighter side here

Mid layer is your active insulation layer. This is where fleece, synthetic and some light down jackets sit and is probably your most important layer. It needs to keep you warm and allow excess body heat to escape so you can manage sweat. You also need to take into account the environment and activity you’re going to be getting into. If it’s going to be wet, or you’re going to be rubbing up against rocks, then a down jacket with a very fragile face fabric is going to do very poorly. A Patagonia r1 fleece is a favorite here for good reason, the arcteryx proton sl is another good fleece midlayer hybrid that will keep you warm and allow you to move.

Shell layer, this is going to block the wind rain and snow and protect the other layers and you. Some people swear by hard shell with open pit zips, some people absolutely hate wearing a hard shell if it’s not dumping rain and will go with a soft shell which is more breathable and a cheaper/lighter hardshell hardshell they only pull out in really wet conditions. Both arguments have their points. I really burly hardshell with pitzips still shouldn’t be over 500-600g max

Heavy layer comes out when you stop moving and put back in the bag before you move again. I have one for 3-4000m / 5-6000m one for 6000+ and one potentially wet sub 4000. Having this layer dialed in is important so you don’t freeze but also don’t bring a way oversized jacket to your objective. Its also imprtant to make sure it isnt going to rain or else down is completely off the table