The point is not about technological similarities at all. It's about who controls the hardware and thus ultimately has the power over its use.

"The mainframe" which the author is talking about is not characterized by COBOL, but by having huge corporations control the hardware which everyone is using in their daily lives, giving them power over everyone.

(A) There are two dominating uses for large computers:

(Use 1) HPC a.k.a. Floating point numbers, Fortran, LLM, CERN, NASA, GPGPU, numerical analysis, etc. These examples all fall into the same bucket at this level of (coarse) granularity.

Dominating use number (2) is accounting. Yes accounting. Append-only logs, git, Merkle trees, PostgreSQL MVCC (vacuum is necessary, because it boils down to an append-only log that is cleaned up after the fact — see also Reddit’s two giant key-value tables), CRDTs, credit cards, insurance, and accounting ledgers.

(Use 2) is dominated by the CAP theorem and favoring consistency over availability during network partitions, because it has to provide and enforce a central coherent view of the world. Even Bitcoin cannot fork too hard for account balances to still be meaningful. (Philosophical nit picking: How does this relate to General Relativity and differential geometry? Can this then only ever be "local" in the sense of general relativity?)

This is where mainframe style hardware redundancy always enters the picture (or your system sucks). Examples: (i) RAIM (RAID for RAM), (ii) basically ZFS, and (iii) Running VMs/Docker containers concurrently in two data centers in the same availability zone (old style: two mainframes within 50 miles and a “coupling facility”)

(B) All other uses like playing Minecraft or Factorio, smartphones, game consoles and running MS Excel locally are rounding error in the grand scheme of things.

Note: Even oxide computers seems to be going down this route. IBM ended up there, because everybody who can pay for the problem to be fixed makes you fix your hardware and processes. Period.

In the end all processes and hardware are locked down and redundant/HA/failure-resistant/anti-fragile. It is a mainframe in all but name by being isomorphic in every conceivable aspect. This is Hyrum’s law for our physical and geometric environment. The other systems die out.

Even Linux user space ABI, JVM, SQLite, cURL, and (partially) JavaScript are so focused on backwards compatability. Everything else breaks and is abandoned. Effectively every filesystem that isn’t at least as good as ZFS is a waste of time.

(C) https://datademythed.com/posts/3-tier_data_solution/

(D) Look at what MongoDB promised in the beginning and what they actually ended up delivering and what problems they had to solve and how much work that ended up being.

EDIT: Add points (C) and (D).

If you want to think like that, you need to factor in the reliability aspect as well. The fact mainframes are still selling well indicates it's very expensive to engineer the 99.999% reliability out of a rack of 1u servers.

Few of those apps are standalone mobile apps. More frequently than not, the mobile app is a thin layer on top of the mobile app.

Based on my reading of the original article, I think your response here might be a bit tangential to the point about offline work? Web apps and mobile apps are both in practice largely the same in terms of who controls the computing resources -- they generally only work by speaking to the remote servers of the company.

But in detail, mobile apps seem like they would have a slight edge for promoting offline work. While they in practice "phone home" (or even store data remotely), they could in principle be written without needing to contact external servers and in a way that all data is stored locally.

I do agree that apps often attempt to silo users and can do this more effectively than webapps, but as used now, both are mostly online tools and so don't really address the question of tools that are usable offline.