10 second rule kill/assist

"The last player to strike the target champion is awarded with the kill, and all contributors within the last 10 seconds are awarded with an assist."

reference: https://leagueoflegends.fandom.com/wiki/Kill

Is this an official timer?

Also does Riot have any ideas of removing the timer all together? It can be very overpowered and can be exploited with long duration skills on characters with damage over time, such as Brand. A long burn timer + 10 second timer can be a death 14 seconds + later awarded in kill count or assist in gold. Also using any Rune skills such as Arcane Comet and Scorch. Does the timer start within or after the last damage effected by damage over time or 10 seconds flat? Either way this always creates optimal situations for these effects to be exploited for champion efficiency.

What design factors are stopping Riot from have a 0 timer? The player would only be rewarded the kill/assist if they landed the last hit. As a last hit for assist wouldn't be counted unless it was actually on point with time. The gold value is why I am bringing this up for as this creates different gold value and some characters will not benefit from this system. Longer damage over time skills are awarded the most gold. In balancing for all characters to benefit I can understand why the time system is placed in the situation to this but time can always be adjusted and/or removed to create a new system/correction which can balance player funding.

I write this to understand Riots design goal as it is currently in place and the game evolves further.