If you just need lower gears, you can switch to 24t inner ring. 24/42 is roughly the same as 30/51. I've played around a bit with really low gears and that's about the lowest gear that is rideable for me. Lower than than that and you have to spin like crazy just to keep the bike upright, walking tends to be faster at that point.
Getting a really light hardtail does make a difference on the hills, but it's not a magic bullet. You have to take into account weight of you plus bike. If you're already at 80 kgs, 2.2kg is only about 2%. My experience is that bang for the buck with bike weight tends to have a cut-off point. Getting your bike below X helps, but anything lower doesn't make much of a difference. Unfortunately, X is different for every rider and can change over time as you get fitter.
As far as upgrades on your current bike, tubeless tires and nice wheels make sense and you can keep those if you decide to upgrade to a completely new bike. Make sure to get future-proof hubs if you go that route. These will have removeable endcaps that allow you to change the hub to various axle widths.
There is a point at which upgrading an older frame design doesn't make sense. 1x gearing and a dropper post make a huge difference IMHO, but neither of those really helps with climbing. They make descending and all-round riding more fun. Given that the reviews of your bike suggest that it has an old-school geometry, I'd wouldn't invest in anything that couldn't be transferred to a new bike.
I recently invested in a carbon hardtail and went from a roughly 12kg full suspended alumimum bike to a 9kg hardtail. I like the new bike a lot more, but I can't climb hills that I couldn't climb before. I just don't have to work quite as hard to climb the hills I can climb. I really like my new toy, but it's very hard to justify what I spent as a rational performance benefit.