The main reason we don't have that (at least for non-private lobbies) is to create replayability in the default game mode, and to create a rubberbanding mechanic to help losing players potentially catch up by picking spells they are more familiar with.
Are you asking for a mode that lets you just straight up pick exactly which spells you want before starting your first round? If the issue is that you don't want to spend a bunch of time drafting spells, increasing the total number of rounds will decrease the percentage of time you spend drafting vs actually fighting.
Also, the 1v1 mode could potentially work for more than 2 players in the future, I just figured there would be too many redundant spell loadouts for it to be fun with more than 2 players.
I have a fun idea for a "booster draft" mode where every player picks from the same "booster" at the same time. E.g. each booster would be randomized and contain 1 primary spell, 1 movem...