I’ve been running the Ultra and am very impressed with the performance compared to the 2013 Trash Can it is replacing. It mostly eats through noise reduction effects like they are not in the timeline. I don’t think the Ultra is completely necessary for only doing HD work, but in my experience, it’s always good to buy the best you can afford at the time of your purchase. Maybe you’ll start to do more 4K work in the future? You’ll be prepared. Yes, there will always be something new coming down the road – new chips, new connectors, new software. Buying the most you can afford will get you through a lot of that.
Regarding obsolescence, I have multiple 2011 MacPro towers with upgraded graphics cards, SSDs and maxed out RAM still running Mojave great. But I can’t run Resolve 17 and some other software anymore, and playing back 4K video on those machines is not ideal. I more than got my dollars back on those boxes and as a testament to their usefulness, I bought what I could afford then and was rewarded for it for many years.
That’s my take. Never buy the base model and get as much RAM as you can. You won’t be sorry with that strategy. If you can wait for the M2, sure wait. if not, you’ll be fine with the M1 Max or Ultra. The performance is ridiculous.