Android's dev team really does surprise me with how bad they are at building an OS. Every single part of the platform is a disaster.
That said, I find that my Samsung S8 has got progressively slower to start apps, particularly, and in that time, nothing else has noticeably changed. I understand obsolete hardware when a load of bells and whistles are added and the old hardware can't do it but I can't see anything noticeably different from 10 years ago.
On the other hand, I can also understand why people don't want to support 10 year old operating systems, which is why I had to bin my perfectly working Macbook Pro once it wasn't allowed to update the OS any more.