Newer hemets vs. older helmets

My Mammut Wallrider is from 2016. When I bought it manufacturers seemed to be starting to think more about side-impact protection, a la swinging into the wall & banging yer noggin, vs. rock fall. Now there's some MIPS helmets too. Have they improved significantly, safety wise, since I got mine?

Improved significantly since 2016? No, mips is a nice addition to have but don't get a new helmet until your old one is really broken. 

Yeah the old helmet I replaced last year was a used bd half dome probably from the 90s I think yer good

The primary function of MIPS is to deal with rotational impact (Mips - Safety for helmets (mipsprotection.com) ):

The Mips® safety system features a low-friction layer inside a climbing helmet that allows a multi-directional movement of 10-15mm on certain angled impacts, intended to help reduce rotational force to the head.

For cycling and skiing, I'm 100% for it and my helmets have it. But for climbing, I have a hard time figuring how rotational impacts could be more important than direct impact. You also have to be aware that it might change the fit of the helmet model, i.e. wallrider will have a different fit than the wallrider-MIPS. Then, for me, it don't think MIPS is worth it for a pure climbing helmet, I would preconize a better fit (priority #1) and if for some reason a model with the MIPS fit me better than the model without it, I will take it.

For lighter helmets using EPS foam, they will most likely be less durable than a hardshell helmet like the Half Dome. Not because the EPS foam degrade (it's a myth: EPS Foam Helmet Liner Performance With Age (helmets.org) ), but because the thinner plastic shell protecting it will be affected by the elements. Also, with time, you EPS foam might have some cracks that are not visible, especially the way climbers could carry their helmet on a pack or with gear. Manufactures might have different recommendation on the lifespan but it doesn't replace a good inspection. You have to decide if the advantages of a foam helmet (lighter and more ventilated outweigh the shorter lifespan).

I personally use a foam helmet without MIPS because it the numerous helmet I tried, it was the one fitting me the best. Along the way, I discovered that I really like the added ventilation and now my hard shell old helmet feel like a furnace. On the downside, it's my second foam helmet because I changed it after 3 years because it was not sure about the foam integrity (100% my fault because of the way I carried it).