it is a mistake, but it certainly shouldn’t cost you the game without so much as a reliable warning, and NOTHING Your enemy can do to win the game should be without risk. MOBAs are all about decision making, there isn’t much decision making involved in “sit by wall, hold trigger until victory.”
I’ve lost maybe two games out of the 200-ish I’ve played because someone did this… each time it’s a momentary lapse of attention, and a very small amount of damage done… but it’s enough. The problem is, it’s not fun. It’s not fun to win that way or to lose that way. It’s BAD for gameplay, it’s bad for new players, it’s bad for the game in general.
The only people who enjoy it are the types that prefer to win with as little effort as possible, have no pride in achieving anything and aren’t here to have fun, but to ruin someone else’s fun.