It's actually the opposite, modern mode uses gpu for compositing, classic modes uses cpu, and any gpu would beat cpu handily in that task including integrated ones.
Unless, you didn't install the correct driver and used standard vga driver, or like in a vm which doesn't provide gpu acceleration.
All valid points but just below that comment someone asked if he/she was reading the new paper (apparently there's an older paper), he/she didn't respond/haven't responded yet.