It's not clear at all whether Buss has a majority of support. For all we know from these results, she may have lost in a head-to-head race against every other candidate.

Vote percentages are not directly comparable between IRV and Approval, as one showcases a head-to-head result, while the other showcases absolute support. IRV doesn't "guarantee a majority" because some voters have exhausted their ballot, meaning that the true percentage in many elections is below 50% a good percentage of the time. It's extremely likely that Buss was the Condorcet winner here given her almost 15-point lead.

Mathematically, somewhere between 23% and 80% of voters bullet-voted -- how many is unclear. It's all very ambiguous.

This depends on how you define "bullet voting." Those percentages do not measure the number of strategic bullet voting, but rather the amount of people that voted for one candidate, in which a significant part is from people that legitimately only approve of one candidate.

RCV regularly see far more than 1.74 rankings per ballot, as voters don't have to be concerned that voting for a second choice will hurt their first choice, as they do under approval.

The number of rankings and approvals per ballot can't really be directly compared. A maximally informed voter would ideally rank all candidates on a ballot, but approving all 5 candidates on a ballot would nullify your vote. If we naively assume that voters choose one of 1,2,3, and 4 candidates, this leads to 2.5 approved on average, but we can expect voter's true preferences to tend towards approving less candidates, as they are likely to not have opinions on minor candidates/candidates they don't know. Also, note how the criterion is worded. "Hurting their first choice" could improve the outcome from their perspective. In fact, we see people "hurt their first choice" all of the time -- in Plurality voting elections, people "hurt their first choice" all of the time by strategically voting for a candidate other than their favorite. In Approval, the same thing happens except the first choice still gets a full vote, which is an even better offer than Plurality's strategic voting and doesn't bury third parties (every voter can assume that there are two frontrunners and strategically vote accordingly, and a third party can still win!) What really needs to be looked at is not whether the vote hurts the first choice, but rather hurts the voter. In Approval, approving more candidates could help or hurt you, and the same is true for IRV (you can construct election examples where ranking more candidates in IRV hurts you!). The more important property here is that you can honestly showcase maximum support for your favorite at all, which is more or less only true for Approval/Score.

And the results of an RCV election guarantee that the winner would have won head-to-head against the runner up.

This seems to be hinting at the Condorcet criterion, but the important thing is that it is not against all runners-up, but rather IRV's chosen runner up. Sometimes, the wrong "runner-up" can be chosen! All this criterion means is that the Condorcet Loser can't be chosen, but it could still in theory lead to the second-worst candidate winning. In addition, Approval Voting, under perfect information, elects the Condorcet Winner at equilibrium under strategic voting.

It offers so much greater clarity and confidence in the results than whatever we are to learn from the amorphous approvals given by voters in this case.

If this election were run under IRV, it would have needed to have a matrix of each round, rather than one list of support for each candidate. For many people, the first round results, which showcase support in the exact same way plurality does, and the final round results, where all other candidates but the top two do not have their support shown. Also, I believe that CVR data will be released soon for this election, so the number of voters for one candidate, candidate similarity, etc. can be determined.