Old blog post benchmarking VSTO and Exes getting formulas in bulk or one-by-one:
https://surrogate-tm.github.io/wmorein/2007/11/13/solution-performance-tip-1-getformulas-and-setformulas.htm
Amazed how slow out-of-process executables are 😱
Also noticeable how Visio's many-shapes slowdown becomes a much bigger issue with 1000 versus 100 shapes, as using GetFormulas (bulk) still delivers much better performance with VSTO 1000 shapes, but not as spectacular a difference as with 100 shapes.
PC from 2007 or earlier, so I wonder how much better is the performance is on a cheap AMD Ryzen 4000 notebook today (or a more expensive Tiger Lake notebook), although I understand older Visio versions may have done things much faster. Why did newer version of Visio slow down so much?
In version Visio 2013 changed engine ! So many users writed about it
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_visio-mso_other-mso_2013_release/visio-2013-very-slow/8b902353-6fb7-49e7-9cee-36ee9fc0c471
https://social.technet.microsoft.com/Forums/office/en-US/2f9b7309-0860-48a3-9bc3-0a19b5302f9f/visio-2013-freezes-editing-drawing
Personally I think Visio 2019 is fine below 1000 shapes, although rendering shapes with gradients in a 500+ diagram could also be faster.
I saw a Microsoft presentation about Visio 2019 where they said they improved diagram rendering performance compared to Visio 2016, I think it was at Ignite when they presented 2019.