First Person Shooter
At 0:22 I can see the box glitch out
While it's possible to iron out most of that jank for a single player game you're going to have all sorts of problems and graphic issues once you take it online. Because it's one of the core forms of player input your players will constantly be using it and will notice every single time it lags behind or glitches up visually. It's not a realiable feature you could base a game around it, at least right now.
you're constantly telling the server new information while it's reacting to your input
It's just something which needs to be handled on the client's side.
That's what happens for everything. Clicking and dragging a box is a sequence of actions with the server reacting to input. Fighting an enemy is a sequence of actions with the server reacting to input. There's no difference.
It's a matter of single input vs continuous input. When you do something like swing a sword you send one command to the server and you're done with it. Sliding around a selection box on the other hand requires a constant stream of information being sent to and from the server.
Each tick requires the server to process the player's input then send the player the necessary feedback. Any time there is a slight hitch in the information stream it's instantly noticeable and instantly irritating.
Okay, nevermind. You are choosing to ignore what I'm saying.
We'll call this other method continuous input, it relies on constant updating.
With continuous input you have a constant stream of instant feedback. While moving around your cursor and updating the laser beam, any small hiccup is noticed immediately.
There's the problem - there's no such thing as this constant updating that you're talking about.
Lag spikes are noticed with the "other" kind of input too and players ignore them just as easily.
When you do something like drag a selection box around you're doing this constant updating which is completely unnecessary.
This is related to the client-side transformation features I brought up a while ago.
You can take any solid color icon and just do a simple scaling transformation to create the rectangle you need for the box selection.