Office has become way way slower, I would mostly put it down to that. Lean applications can still start pretty fast. One other thing making it slower is antivirus software scanning every binary you run before it opens, including Defender. Turning off Defender is a reliable way to improve app load times.
But I've compared how long it takes to start Word on my Pentium II 450 MHz running Windows 98, with Word 2000, to my Core i5 2500 K (3.3 GHz) running Windows 8.1, with Word 2010. The Pentium II wins.
I don't how much of the difference was Windows versus Office, but it's a sad indication of the slowdown in software outpacing the speedup in hardware.