You forgot "runs on Mac and Linux, not just Windows" as well as "includes source code". 
(I think being Windows-only is a rather large indictment of their methodology vs. claims made so far.)
Long ago they mentioned a PARSE /TRACE refinement which takes a callback function. Current Red reports the callback signature as:
/trace =>
callback [function! [
event [word!]
match? [logic!]
rule [block!]
input [series!]
stack [block!]
return: [logic!]
]]
But because DiaGrammar is not open source we don't have immediate access to whether it uses that. And because Red isn't LGPL'd we don't know what kind of hacked up version of Red they have; it's not a proof of what the language itself is capable of as pitched.
(I explained my rationale behind LGPL'ing Ren-C a year ago. People shouldn't look at it as "restricting their rights" to distribute their binaries without source... but rather as making a promise, that Ren-C won't be enhanced and folded into some project without letting you know what's going on...leaving those who've bought in without support...)
Well this is why they have to cut features in PARSE. If it had too many features it would be too slow to run in a loop.
(In case you missed the UPARSE performance post...)
Small price to pay for solving COVID-19!
If programming history looks back on them and scoffs, they can't say I didn't warn them...
I think the slow-and-steady scrutiny of things piece-by-piece is really the only way to get to the future vs. repeat the past.
And I'm not giving up on Ren-C. In fact, I just got back to my coding bunker after a couple months of enjoying what will likely be a narrow window of coronavirus freedom. I will be digging in for the rest of the year, seeing how much I can get done.