Related tasks:

• T410513: Parsoid behaves strangely on pages violating the Expensive Budget "expensive-parserfunction-category" BUG discovered the same day
• T376564: Scribunto should provide a bulk ifexists check resolved

Is there a practical use case where it creates an issue? newBatch() is intended to help avoid hitting parser function limits, but if you are really going to abuse it for 7000+ page lookups, it'll inevitably hit some limit or another. That's not a performance issue, it's the system working as intended to prevent excessive load.

Reportedly LUA can use 50 MiO RAM, quite generous. But if 7'000 pages hog 50 MiO, then every single page consumes ca 7 KiO. Does it really need so much? I could try to call "mw.title.newBatch(...)" in batches of 25 pages, and copy the relevant info from bloated title objects into a LUA table of booleans.

I ran a little experiment: the lua module at https://en.wikipedia.org/w/index.php?title=Module:Sandbox/SD0001/ext&oldid=1323886587 has functions to show the existence status of 500 pages, with and without use of newBatch().

{{#invoke:Sandbox/SD0001/ext|batched}} consistently gives a Lua memory usage of 4.1 MB.
{{#invoke:Sandbox/SD0001/ext|notbatched}} consistently uses 4.2 MB.

So, batching uses the same amount of memory, if not marginally lesser, than creating mw.title objects manually.

In T410527#11399132, @Taylor wrote:

Reportedly LUA can use 50 MiO RAM, quite generous. But if 7'000 pages hog 50 MiO, then every single page consumes ca 7 KiO. Does it really need so much? I could try to call "mw.title.newBatch(...)" in batches of 25 pages, and copy the relevant info from bloated title objects into a LUA table of booleans.

I would suggest batches of 500 rather than batches of 25.