As Points Scrounger implied above, the limit is more of a per-country thing (if you're using a card instead of a device) and not dependent on other factors--for the most part. CDCVM/device authentication is something that may be merchant dependent, especially if they're still running older terminals/software that aren't set up to support it. However, for those that don't support it, that just means that the contactless limit for devices is the same as with cards.

In practice, though, the vast majority of terminals outside the US support transactions over the country's respective limit if you're using a mobile device. And if you run into a place that doesn't, you'll still be able to avoid signature for smaller transactions.

BTW, Strong Customer Authentication in the EU is going to go into effect later this year that will change some things in regard to how contactless works for EU residents. It remains to be seen if anything will change for Americans or other visitors, however. If nothing else, the limit will go up to €50, so more contactless card transactions may be possible without insertion/signature.

There aren't any transaction quantity limits, or really any limits of any sort. There's not really a reason to have them, either, as you've mentioned.

EDIT: I forgot to mention that in some cases in the US, the no CVM limit for contactless is $0 (this is much different than the limit after which contactless is no longer possible, of which there is none). There's a lot of technical details I could go into about that, but in short, it's due to the terminal allowing tap without knowing the final purchase amount--hence applying the usual no-signature/PIN waiver is impossible.

That said, since signature also isn't required anymore, this probably won't be an issue for the typical signature-preferring US credit card. However, it might be for debit cards, especially if merchants would have otherwise routed a debit card transaction over Visa or MC due to it being a smaller transaction.
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As mentioned a bunch of times before in the US contactless thread, I suspect this isn't actually the case for a few reasons:

1. There were never all that many cards floating around a decade ago to cause the supposed paranoia. For most Americans, their first introduction to contactless was mobile wallets.
2. Contactless isn't avoiding security features that would have otherwise been required (e.g. PIN).
3. Chase and other major issuers considering or are currently rolling them out would have shut that idea down very quickly if it meant losing a large number of customers to other banks due to their concerns about security. In fact, if mobile wallets were more popular, I suspect contactless cards never would have been a thing simply because they'd be able to avoid the extra per-card costs for contactless.

BTW, issuers that are rolling them out seem happy with their adoption from what I've read and heard. At least in comparison to mobile wallets.

If online PIN is supported by the terminal, it's possible to type the PIN after tapping without needing to insert. Granted, there aren't that many countries that support it (and the US quite possibly won't support it for contactless outside of domestic debit cards).