It's actually getting faster.
The blockchain does not increase largely over long periods of time, in 2014 it was less than 200gb, ten years later, it still hasn't gone over 600gb. Download speed on the other hand is developing much faster, ten years ago 2-5 mbs was considered fast, today 500-1000 mbs is what's considered fast for most and some service providers can hit more than that.
- Jay -
Download or Upload speed has never been a factor since Bitcoin Core IBD is parallelized to different peers and it has never been the bottleneck of IBD ever since its introduction. Besides, your bandwidth benchmark would be a naturally inaccurate metric since it also depends on the upload speeds of your peers.
As mentioned previously, Bitcoin Core is heavily dependent on I/O, CPU and RAM. Ideal situation would be to just keep the chainstate in the RAM during IBD, and thereby negating the need to flush them frequently. Signature validation can possibly be a bottleneck on a slow CPU, fast I/O and sufficient ram since secp256k1 lib is quite optimized already. Else, your I/O and your ram are the likely bottlenecks.