Tax strategy is big and complex, as you've already alluded to, OP.
Traditional IRAs are just deferred income. So if regular income is high in a given year, contributing to a traditional IRA can lower the amount you're taxed on -- but only for that year. You have to pay taxes on it eventually; you just try to plan so that you're taxed at as low a rate as possible on that money. For me, that's up to 12%, at least until 2026, when I believe the 12% bracket reverts to 15%.
If regular income is low in a given year, you probably don't want to dump it all into a traditional IRA, because there's less or no tax benefit. It all depends on the bigger picture.
And yeah, ACA subsidies factor in too, based on taxable income for the year. But remember to compare the subsidy against any higher taxes you might have to pay when you take that money out of the traditional IRA. If you'd get $10k in subsidies, but it ultimately costs you more than $10k extra in taxes, the subsidies aren't really worth it. Right now, the bracket after 12% is 22%, so you could pay a whopping 10% extra in taxes if that money ends up being taxed in that higher bracket. Tax planning, including for subsidies, is a very long-term process.
I see Roth as the promised land, where I want to shepherd all my money to eventually. Once it's in, it never gets taxed again.