No, I don't think it's only about "more complex websites", "more taxing multimedia" and so on - it's more likely also macOS and Windows bloat and questionable software quality getting in the way. I recently installed Ubuntu Linux with the LXQt performance-oriented desktop environment on a 10-year-old Intel i7 2600 workstation back from 2011 (16 GB RAM, an Intel HD Graphics 2000 built-in GPU, an Intel SSD with specs archaic by today's standards) and the system is extremely fast and responsive at everything including web browsing, multimedia playback, IDE-based development (e.g., CodeBlocks), app launching, etc. Website content and multimedia rendering alone is not enough to saturate even a 10-year-old CPU/GPU.