Short answer: yes its fairly normal to not hit 70° with a good gpu cooler and decent airflow.
Longer answer: Try running furmark or a similar gpu benchmark that lets you monitor clock frequencies and power draw. That will let you see if you have any kind of actual problem or not. If there are no dramatic reduction in frequency/fps/powerdraw, theres nothing to troubleshoot.
I would not plan to buy any specific GPU expected to be released in the future. If your 3070 is struggling now, now is probably the time to upgrade. But if you want to wait until better price/performance options are available, you probably dont have to wait for 5070 series. Radeon 8000-series will probably launch this year, and even if Radeon 8000 isnt quite your cup of tea, it's likely to trigger price drops for GPUs like the 4070 Ti Super.