I'm totally sure the RSA operations are using the AES instructions
> Try using your old 2003-era system to generate keys again and tell us how fun it is.
generating (fresh) rsa keys? you don't do that on connection to a SSH server
as for what actually happens on connect, 2004 laptop: 33 signatures/second and 2200 verifications/second (+DH/ECDH)
the RSA operation (verifying the server's host key) took a total of 0.0005s
even my raspberry pi 1 can do 240 4096-bit verifications/s and several thousand ECDH's/second
and I have yet to see a SSH server with 4096-bit host keys
tldr: even old computers are fast (and data > supposition)
The Rpi? For FFS, an Rpi B+, a PSP, or a 2003 Athlon XP could emulate a System7 era Mac with a Quadra setup without a single slowdown.
I told you to get off my lawn.
I suggest reading up on how the SSH protocol works
We don't realize it, just as someone using a text terminal may have not realised it between 1985 and 1995, if every response after a key press was already instant.
For typical GUI interfaces, tasks like tossing video data around, and so on, computers became approximately inifinitely fast sometime c. 2005 - 2010.
The most powerful Power Macs with non Intel CPUs were discontinued in 2006. (G5, released 2003.) [2]
Your laptop from 2014 was already running at LEAST a 64bit CPU and likely has AES instructions as they were introduced in 2010 [3]
So even if your laptop from 2014 onward didn't include AES instructions like some Intel Atom/Celeron/Pentium models... (Acer C720P Chromebook, for example came out in 2014 and has a Intel Celeron 2955U [4] and [5]) It was still an architecture that is/was ELEVEN YEARS NEWER. A Celeron 2955U is roughly equivalent in performance to a Core 2 Duo E4700 or an AMD Athlon 64 x2 5200+ ... which is still quite ahead of a PowerMac G5. [6] and [7]
TLDR: Time marches on and along with cpu improvements come instructions and other benefits not immediately visible to the end user.
Try using your old 2003-era system to generate keys again and tell us how fun it is. Bonus if you try it on a Pre-2000 era Performa Mac as a user typically had with SystemOS 7, 8 and 9. Those ran at 16 to 66mhz. [8]
For reference, SystemOS 7 came out in 1991. [9] OS8 came out in 1997. [10] And OS9 came out in 1999. [11]
The CPUs inside the Performa Macs running System 7, OS8 and OS9, at best, can be compared to the 486s on the Intel side. Not even Pentium level. This places the architecture at LEAST a dozen architecture generations behind what you're generating keys on. This means if the CPUs we're looking at here were aged up, your laptop is starting first or second grade while the actual CPUs of the time are now finishing their masters' degrees with a kid or two on the way.
Rather than naively using your extremely modern in comparison 'crappy laptop' cpu as a reference point, perhaps you should use something more typical from the time these OSes were considered relevant.
TLDR to the TLDR: Get off my lawn.
[1] https://www-01.ibm.com/common/ssi/ShowDoc.wss?docURL=/common...
[2] https://en.wikipedia.org/wiki/Power_Mac_G5
[3] https://software.intel.com/content/www/us/en/develop/article...
[4] https://www.amazon.com/Acer-C720P-2666-Chromebook-11-6-Inch-...
[5] https://ark.intel.com/content/www/us/en/ark/products/75608/i...
[6] https://www.cpubenchmark.net/compare/Intel-Celeron-2955U-vs-...
[7] https://www.phoronix.com/scan.php?page=news_item&px=PowerMac...
[8] https://en.wikipedia.org/wiki/Macintosh_Performa
[9] https://en.wikipedia.org/wiki/System_7
[10] https://en.wikipedia.org/wiki/Mac_OS_8
[11] https://en.wikipedia.org/wiki/Mac_OS_9