Sure, but if they modify the AGPL they need to disclose that prominently in the program or service covered under AGPL, similarly, if they incorporate such code in their own, possible non-AGPL code (e.g., GPL) the combined code base will become AGPLv3.

But sure, given that you upheld to the licenses rules, like the notice of any derivation/change, you can still provide commercial service just fine.

The "power" of the AGPLv3 is that no company can just "steal" your AGPLv3 licensed project, change it to make it seem like it's theirs, and provided it as a service without telling anybody about the actual origin of the upstream project nor laying the changes to contribute back to upstream; something that the GPL would allow (for SaaS like offerings); that can still be a huge advantage for startups; if it's the right choice depends a lot on the product and intentions of such a start-up.

(the quoted words are there for a) not a native speaker, so avoid reading too much into my wording and b) stealing is rather a harsh term I don't like to use in connotation with (free) software code)

From a commercial standpoint it's irrelevant what the license "intends." All that matters is what the legal department thinks will happen in the worst case, and for GPLv2 or v3 the "worst case" is all that proprietary software that the company wrote on top of it is now publicly available for free to any end-user.

The claim that GPLv3 is the future of open source licenses is laughable. There are going to be a few idealists licensing their software using GPLv3 but that software won't gain significant traction in any sort of commercial setting, outside of a few exceptions. Just take a look at the software libraries that get widespread use today: the vast, vast majority of it is Apache-, MIT-, or CC-licensed. GPLv3 is going to end up being a historical footnote at some point, because economics trumps ideology every time.