The thing about using the word "literally" and emphasizing words with caps is that they in no way make your statement truer than it is. :P In answer to various false guesses such as yours my lovely guildmate did the following model:
The setting: we are looking for how many weeks it will take for a character to fill up all its gear slots only using the M+ chest. The chest currently gives a choice of three items (compared to BfAs one item) of Mythic Raid ilvl. We assume that the type of items are selected randomly.
What we simulate: the number of weeks needed to acquire at least one item for each slot from the M+ chest. For each set of choices (1 choice per week, 2 choices per week and 3 choices per week) 100,000 simulations, each corresponding to one character's gearing path, were run.
Results: If we suppose that three choices are given each week, on average it would take 23.1 weeks (std = 5.3 weeks) to cover all slots. If we suppose that two choices are given each week, the average is 29.4 (std = 8.3 weeks). Finally, getting one choice per week (current BfA system) would take on average 49.8 weeks (std = 17.5 weeks).
I have provided histograms below for each case to give a clearer picture. To sum up, the multiple choices provided greatly speed up gearing compared to BfA even if you only use M+ dungeons to do it -- which is good thing for most players. The effect is pronounced even if you don't run too many M+ dungeons -- running 4 of them already gives a choice of two items which greatly speeds up gearing.
Finally can also add that naturally, the fewer the choices, the higher the variation (standard deviation) of the number of weeks required.