When switching from film to digital, we took a lot of steps back and are slowly catching up to quality. I guess around the 2010s, theaters started switching to digital projection, which I believe started with 1K (similar to 1080), then 2K, with a small amount of theaters showing 4K projection. Most high-quality 35mm film is equivalent to 4K resolution. Unfortunately, a lot of movies were shot and mastered at 2K or less, like Mad Max fury road, so there's no point of having them at 4K because the information was never there. With old 35mm, it was probably scanned for dvd or vhs at some point, but studios are going back and scanning movies to 4K with great results. Megapixels aside (an irrelevant number btw), dynamic range was pretty bad compared to film in the early days of digital, but it's starting to get there. The revenant was shot on digital and looks amazing.

Once you start watching on streaming though, you're losing so much to compression. Even with 4K HDR blu-ray, you're only getting 10 bits of color compared to 12 bits with DCP (digital projection).