Macbook Air 2018 - too hot to touch, battery life poor

First time Mac complainer after 20+ years using them.

1. It runs unpleasantly hot, even just during normal browsing (Firefox) and typing (TextEdit mainly). When downloading, it gets hot to the touch, with the keyboard leaving the tips of my fingers uncomfortably hot. According to Activity Monitor, Firefox and Firefox web content are claiming more than 70% CPU usage, which probably accounts for the heat. When using Scrivener and Logic Pro X, heat radiates out of the machine. After half an hour browsing and typing, the whole body of the machine is uncomfortably warm to the touch, especially underneath, keyboard and 'wrist rest' area.
2. I'm watching the battery ticking down even during browsing and typing (I use TextEdit mainly), with 10%-15% gone after 1/2 hour browsing with Firefox and typing with TextEdit. When using Logic Pro X (yes, I know - see 'heat' above - but I can't afford a MB Pro), or even Scrivener (my preferred writing app) it ticks down even quicker.

I consider typing and browsing the bare minimum a machine should be comfortable handling, and it shouldn't cause me discomfort. I've used Mac laptops since 1996 and this is the first time I've noticed heat as a problem in a new machine.

I'm pretty disappointed, bordering on regretful right now. I could have snapped up an old Air for £600 cheaper...

Question: are the issues I'm experiencing grounds to seek a replacement machine? Is anyone else

experiencing these things?