Yeah, nowadays they have decent speeds, but I remember years ago I was struggling to get even 10mbit out of their servers, I even had to switch to a different location in steam settings to get somewhat better download speeds.
Transfer speeds from Steam have been great as long as I have had FiOS:
- 35 Mbit/s full duplex (~2009-2011)
- 150 Mbit/s full duplex since (~2011-2017)
- 940/880 Mbit (marketed as Gigabit full duplex) since ~2017
In all of that time, I've been able to download games at something like 98% of my available local WAN bandwidth.
Been maxing out Steam downloads at ~117 MB/s since 2017.
I've been on Steam since close to the beginning (I didn't join immediately as I was happy with Counter-Strike on WON) but as soon as the Counter-Strike: Source / Half Life 2 bundle went live in early October 2004 I joined to buy it (Still the only time I've ever pre-ordered

)
I can't remember how fast that first Steam download went, but as I recall they had a pre-download which they made available in tranches as the release date got closer, so maybe that helped alleviate download speed issues for that first one. This was the only Steam game I had for years after.
I honestly don't remember a time Steam has ever had anything but strangely impressive download speeds, though for many years there I probably didn't have the best internet connection to really challenge it. Internet didn't get good in my neck of the woods until Verizon brought FiOS here in 2009.