I wanted this feature for a long time now and I'm glad to find the exact same idea on this post. It's quite sad it wasn't implemented yet
Most of the time, my legend is available and I don't interact during this phase. I use to go to the bathroom or get a drink during the selection, with the headset still on the head so that I can estimate how much time I have before the drop, just listening at the sound of the loading screen, champion select, boring here are your champion screen, countdown to the game, even listening if I'm the jumpmaster or not (only to be able to run to the computer before the end of the countdown if I am). Champion select is actually so fast during this long wait that this is not even possible to involve with the team a that point IMHO, it is not a league of legend style where we have time to find a nice comp, communicate (and get insulted yes). Even when I am on the select screen and I notice my legend is taken I barely have the time to find the second one I would play since it is not so frequent and since this phase is quite boring I'm on my phone.
I don't mind playing another legend but there are some I'm really bad with and I just don't have any fun/muscle memory playing them. Meaning I have a bad game, no fun, Im frustrated to do * and make my team lose. After 10 game in a row without issue, I sometimes have 2-3 of them where I have a * random selected legend. And then, I have to be honest, finally rage quit and leave my team alone, even I really don't like doing that. I would certainly die at fist fight anyway trying to smoke the team and using my bracelet inside the fight or pulling out my drone.
I regret buying some of the legend I have just because of that, and I stopped buying any of the new one even if I have enough token juste to have less chance to have a legend I'm not used to in case there is a random select.
I can understand that you don't want people being AFK at drop phase but in my experience if someone is afk, he is afk. I won't chose his champ, and won't be jumpmaster either. No mater if he is the first or last to be randomly choosing his champ in the selection. It already append to me, got distracted during the loading and didn't notice it started. I was still the jumpmaster If you want to be sure that the jumpmaster is the best one, just chose one that is active in the menu (even moving the mouse) and maybe add a preference for that too. I don't chose my legend also because I don't want to be the jumpmaster.
The last legend is selected by default. If you want the player to be involved, during the selection, Why? Because it is a nice quality of life. A nice INCOMPLETE quality of life. This just needs to go one step further.
I'm sure this will implies less leavers at the start of a game.
I mean, even the skins have a random favorite selection. Not the best solution but this would be ok: set favorites legend. If last used is not available, select a random one in the favorite legends. (Ranking he 3 favorites ones is actually a better idea but this at least would avoid having a legend we really don't want to play and allow to buy the new one without fearing a backfire if we don't like it.)
It would even be a way to randomise between favorite legends if wanted
If I had to make a quick spec about that would even group multiple use case, it would be that middle clicking on a legend would cycle true 4 possible levels. Nothing, first favorite, second favorite, third favorite. (with little stars or stuff to make it cool and visual)
It would be completely possible to have 5 first favorite: It will pick randomly between one of the available ones.
It would be possible to first have two first favorite, and one second favorite. Will randomly pick one of the first two, and if not available, the other one.