Is there any point of caseless guns?

caseless ammunition is already a thing among tank guns

Every single time.
First no. Brass cases take out a single digit percentage of heat from the rifle. You can do the math yourself if you like. All you need is the temperature of the case after firing, the weight and the specific heat of brass. Yes the effect exists, yes some heat is voided that way, but its basically negligible for this purpose.
>But user why was cook off such a problem then?
Because brass is thermally conductive and chamber temperature isn't perfectly even. Uneven chamber surfaces from defects or damage, variation in combustion etc can cause sections of the chamber wall to be hot enough to ignite the propellant even when the average chamber temperature is below the required threshold.
When the propellant block is in direct contact with the chamber wall, this means the small part contacting that hot section can get hot enough to ignite and start chain reaction, cooking off the round even when the average chamber temperature should mean it safe.
Brass helps this by being thermally conductive. Heat will spread around the case as it transfers from the chamber to the propellant, averaging out the temperature over the whole case, meaning your average chamber temperature is now directly representative of actual cook-off chance.
If you think about it, it makes sense because the G11 didn't have any significant heat issues after they switched to HITP.

Ok, retard