It's serious, completely serious, give top level 1v1 players 65 muni demos even with a 3s timer and watch the world burn.
The problem with demo changes is not that they are nerfed or buffed. The problem with demos is that this change completely flips upside down what they are supposed to be used for - at least on paper, the consensus seems they are there as blobbing deterrent.
This change will completely remove the blobbing deterrent part while on the other hand they will still be used to wipe capping squads even at top level play and for much lower cost, as you correctly state.
So no, people are not complaining that it is a nerf. For a change that supposedly aims to fix one-click-wiping unsupervised capping veteran squads, this change actually "fixes" i.e. removes all other potential uses of the ability while simultaneously doing
absolutely nothing to solve the one-click-wiping of unsuperwised squads and in fact pigeonholing the ability into being used in exactly this way.
Sure there are more things you can do now against stationary structures. If you have 200 ammo you can place 3 charges in place of 2. Some cheeky smoke play vs the Schwerer comes to mind.
Ultimately I am not an authority on what demolition charges are meant to do, so I can't say that the modding team has it right or not. I am personally glad that at least some change has been made. Anything is better than what we have in place currently.
Actually back in the day I proposed a delayed detonation after you click, let's say 3 seconds, but the timer is invisible to the enemy. The price would remain unchanged. That still doesn't solve the lone capper problem but it would allow blob punishment. And unlike the current change, noone can call it a buff - it would be a straight up nerf.