I think with adjustments, this is the best way to continue the format without as much problems from the power creep.
The simplest adjustment would be Vintage with less than a 4 per card max. 1 may be slightly too restrictive, but 2 or 3 card maxes could be a better compromise keeping the restricted list such that some cards are 1-ofs. This may not go far enough though and we could still end up with power creep problems.
Another way around killing decks is to allow any card, not just legendaries, in a modified “command zone”. E.g. Each player can set aside 1 card at the beginning of a game (or tournament, or match if we want to be stricter) and guarantee that card in their opener. The other 6 cards are then via standard mulligan rule.
This also allows some balancing of the play-draw rule as the player on the play would have to fetch their card up first and say reveal it. An opponent can then fetch up a counter strategy if they wish. E.g. I get Bazaar on the play, my opponent gets Leyline on the draw.
Certain cards could be banned from being able to be put the command zone in order to balance this format mechanic (e.g. ban Black lotus from the command zone).