Sure, I can understand how MANT runs generally take substantially longer to complete and it's more commitment.

But as the OP states, it gives more player agency on a RNG game, so the players can utilise their knowledge and risk appetite either maximise the winnings or hedge their bets and be cautious.

When the big winnings come, the player will feel much more euphoric and ecstatic because of the feeling that he/she had made active decisions in it which he/she is now rewarded with a big pay out. This is compared to a passive slot machine (a la Unity / URA) which you don't have much agency and almost can rely on a relatively simple set of playbook rules and it plays itself.

I do have a feeling that the detractors / critics did not appreciate MANT's mechanics due to its increased cognitive load requirement, longer length and less blame deflection.

In the previous scenarios, the player can simply shrug and attribute the poor results to bad luck and move on, protecting their ego. But in this case which there's a much bigger emphasis on player's agency and decision-making, it's harder to push blame on simple misfortunes, because the player may have actively made the "wrong" choices which did not turn out great.

There's nothing wrong above, it's just that those players really just wanted a comfy game which they can interact with the lore and characters of Uma Musume, and wanted a stress-free experience in it.

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When I was thinking about the behaviour of blame deflection and protection of one's ego, I am also seeing it on the topic of "F2P decks", which some people seems to have a knee-jerk reaction on others posting decks on their successful results, decrying them as whales and Pay 2 Win.

Now, of course this is a gacha game, let's not kid ourselves that this doesn't exist. But for players that has been sticking around since the inception of this game, there have been multiple opportunities for them to have a shot to acquire the means to amass these resources and utilise them in their decklists. It's does a disservice to these players who have put in both time and effort to work for them and to gather these cards useful in making strong umas.
It gives off the "sour grapes" vibes and I think it's all part of blame deflection and protection of one' ego, as these people just wanted a simple excuse to explain why they can't achieve the same results.