This is true, but then again, Riot's been trying to bring average game length from start to finish from the 45-minute mark to the 30-minute mark. At its worst, the lobby lasted around 6 minutes, so while halving it is huge progress, it nonetheless doesn't give actual matches enough wiggle room to last longer and still hit the intended mark. Whether or not that mark is justified is up for debate, and largely questioned by many players, but the official goal seems to be to reduce game times across every facet.
With that said, though, one aspect of game time that I feel hasn't been touched is connection time. For every match, there are around 1 to 3 minutes of waiting time as the game loads the map and every player together: I'm not familiar with League's tech, but I wonder if it would be possible to begin pre-loading the map and other related assets during the lobby, since at that point the map and teams are already set, and champions and loadouts are the only variable (which also get locked down as players select their picks). If it is possible, and if it hasn't been done already, pre-loading the game for everyone in the lobby could help shave some more waiting time off of each match.