> Few people in the church, including the priests themselves, are fluent in Latin (there's a story told, I think by Francis himself, about an diocese in England that required priests to pass an exam to give a Traditional Latin Mass, and almost none of the requesting priests could pass).
Strictly speaking, as well as the Tridentine Mass, one can also have the current Mass in Latin. From what I've heard (never been to one to experience it first hand), Opus Dei centres worldwide say it almost every day. Outside Opus Dei, I believe it is quite niche – but, strictly speaking, all Catholic priests (of the Latin Church, or Eastern rite with Latin faculties) are allowed to say the current Mass in Latin, and Traditionis custodes didn't do anything to change that. I think few are interested, and from what I've heard, to try to prevent people shifting from Tridentine-in-Latin to current Mass-in-Latin, bishops have been quietly instructed by Rome to disallow it in practice, even if it is still formally allowed on paper. However, if a priest wants to say the new Mass in Latin privately, or to a small group which isn't widely advertised and flies below the radar, I think that is both officially allowed and likely in practice too. But, the linguistic competence concerns you mention about Tridentine-in-Latin apply equally to current Mass-in-Latin.
Quite separately, there is a history of the Tridentine Mass being translated into other languages, both in some cases authorised by Rome, and also by external groups such as Anglo-Catholic Anglicans, Eastern Orthodox, Old Catholics, Polish National Catholic Church – I think all the cases of this in communion with Rome have all effectively lapsed through disuse. But still, it is another reason people ought to avoid equating Latin and Tridentine.
> The TLM obscures what the mass is about, which creates space for practitioners to substitute in their own things, which, as it happens, tends to be idiosyncratically ultra-conservative stuff. The church is a top-down institution, and the TLM gets in the way of that and divides it.
I think a big potential problem with what Pope Francis did – it made no difference to the quasi-schismatic SSPX, or the more explicitly schismatic groups to their right, who were very used to ignoring everything the Pope said (except maybe if they liked what he was saying on that occasion) – but it upset that minority of Catholics who were involved in the TLM within the Catholic Church proper, and potentially drove them into the arms of those more schismatic groups. Now, to what extent has that potential been fulfilled in practice, I don't have enough personal experience of this topic to say–but I'm sure it has happened in some cases, however many. And I know there are even quite a few conservative-leaning Catholics who weren't involved in TLM in practice, but found the decision upsetting, and it might increase the odds of them wandering off as well.
Of course, the people we are talking about are a small minority in comparison to over 1 billion Catholics worldwide. But most of that one billion are far from devout – people who rarely attend Mass. At the more devout end, at least in some geographies, those involved in TLM, or who aren't but were upset by this papal decision, are arguably much more significant. And much of the institutional strength of any religion comes from its devout minority, as opposed to millions of people who identify with it at some level but far more rarely actively engage with it.
So, I think even if one doesn't have any personal affinity for the Tridentine Mass, there are genuine reasons to question the prudence of this decision.