You think a car gearbox is heavy, try bench pressing a Land Rover gearbox up off your chest and into position.
Most jobs on a car are do-able at home if you have the right tools and do your research beforehand. IME there are lots of scare stories on t’internet from people with zero mechanical experience who have attempted things they really shouldn’t have. In reality it’s just a case of knowing what bolts to undo and in what order.
I find car stuff all rather small and mostly not much more than finger tight, but 95% of my tinkering involves Land Rovers, grinders, welder, big hammers and man sized spanners.