Shocker.
I'm fortunate in that I do computer hardware repair ... so I approach this from a perhaps an additional approach of simplifying the questions and looking for paradoxes.
I BELIEVE... the problem with "lag" of any amount, is that the cameras HAVE to be cheap for us to buy them and perceive them as good "value."
The companies have to have lenses, software, marketing, websites, etc.
We look for specifications when we purchase... and we purchase based off the specs that we KNOW about on the line item list.
What doesn't go on the line item list of a network surveillance camera? The processing power. The speed of it to encode RAW video... in to H.264 in the incredibly high FPS and resolutions we want... let alone, H.265. Can ANYTHING do this instantaneously? Really. Try your 3,000 computers guys... just PLAYING BACK a high speed, high res stream will make your fans go nuts.
These cameras don't even have fans.
And they have NO BUDGET for a CPU... They rely on a SoC... and a CODEC (coder decoder).
I purchased an expensive camera by samsung... lag time, shorter. I have some knock off stuff I want to get rid of... you think they have the same lag times? on the SAME network?
No.
These are the soft, unspoken differences professionals who get to play with everything know.
Suckers like me, on a budget, unable to try EVERY product? They count on me assuming it's something I can't debug.
Try lower resolutions... and you'll think your network was the problem; not the change in complexity of performing the algorithm on the CODEC that is transcoding the video to a small package that'll fit over network... instead of RAW, UNCOMPRESSED 1080p which could be a few hundred MB/s (capital B)... which your 1000Mb/s networks will not do.
So, its time we search for things based on the codecs processing power, not just the resolution, lux, etc.
Hope that helped and isn't wrong for 100 reasons.