What about Gradient Lag?

What are you talking about? You're just overstating. To me climb pro always announced a climb before I stepped into it. Maybe climb longer climbs too.

Also, there's no such thing as gradient lag, it's a normal behavior I believe. I've owned 3 different garmin devices and not even counting watches, and the gradient was always displayed late. About 10 seconds or something like that

1. Not arguing YOUR unit works properly. Mine plus hundreds of others are NOT. I bike in two different areas in the last 30 days (Sardinia and France) and my 1040 was ridiculously wrong on gradient,  position during the climb , temperature plus many other issues 

Some users don't know how one device should work, and they take everything as granted, even lag  

I had Edge 810 , 705, 1030, non of them had any lag issue.In the beginning of  1030 they removed decimal from the gradient, and then there was some lag, but nothing critical

Yes agree

All devices have this delay yes, but it's not just about gradient, it does behave the same with altitude gained, D+, speed, (if you're not using a sensor that is)

What do you mean by wrong on gradient, delayed?

I upgraded to the 1030+ and had serious lag so when the 1040 came out I bought that and sold the old device and guess what, same or possible worse lag.   Previous Garmin devices were perfect for gradient.  Come on Garmin fix this problem, also why develop a new device with the SAME PROBLEM!