Can I combine two 12-2 cables to serve a NEMA 10-30 socket for dryer?
Are you trying to break a record for &quot;most code violations&quot;?  Code exist for a reason, the reason is safety.  Tech is supposed to serve us, not kill us.
Your entire logic is that &quot;Code is a bunch of nonsense legalese&quot; simply because you don't understand it.  No, every rule has a safety reason.
Further, you have a bunch of beliefs that are wrong.  And all your beliefs happen to support your plan.  Coincidence? Not. You are &quot;making these facts up&quot; to justify what you want you do. That's the road to perdition.
NEMA 10-30 receptacles haven't been legal for 30 years.
Old ones that were installed properly prior to 1990 are grandfathered (you don't need to rip them out) but you're certainly not allowed to install any new ones.   All dryers which might plug into a NEMA 10-30 are required to use a 14-30 today, and all are able to do that.
NEMA 10-30 has a neutral. Not a ground.
Neutral is not ground.
The whole problem with NEMA 10-30 is it doesn't have a ground.  That pin you think is ground is actually neutral.
All the dryers you think don't need neutral, actually do need neutral.   They are using an archaic exception in Code that allows plugging them into legacy NEMA 10-30 sockets if the socket was installed over 30 years ago.
The reason usual/cheap dryers need neutral is they have 120V tumble motor and controls.  I don't know why they don't just make those 240V, SMH, but that would cost $10 more, and we can't have that!!  They also use electric resistive heat strips to dry the clothes, which is the most expensive and inefficient way to do that thing.  Cheap to buy, expensive to run.
If you want hot-hot-ground, use NEMA 6. But most dryers can't use that.
For instance your 12/2 cable could support a NEMA 6-20 recep, which indeed may be able to feed certain high-tech dryers such as the condensing types you don't like for some reason.  (perhaps you do not pay the electric bill).
It doesn't cost $5000 to run a branch circuit.  5000 pesos, maybe.
Paralleling is right out.
It requires special equipment on the supply side that is specifically UL-listed for paralleling. That means it needs to meet the safety regs in the UL White Book also.  Also paralleling is not allowed below #1/0 wire size (125A), and realistically nobody does it below 4/0 (200A). So you simply won't find appropriate equipment, nor would you want to pay for it if you could.