Nice one...
Subtitles should be clear and easily readable and understandable for everybody.
I think pretty much most people understand the "=" symbol. Maybe the same for ">". So for those to examples it wouldn't matter too much (although I think words look ' nicer', the same like "
Here are two examples" looks nicer than "
Here are 2 examples").
But what about more 'advanced' symbols, like infinity (∞), similarity (~), identical (≡), difference (∆), etc.? I think for those you would definitely be better off with writing them in words.
Also, subtitles have limited available time and space.
So here is a problem: what about if there is not enough time or space to use words? Or complex stuff like ∑ xᵢ = x1 + x2 + ... + xn ? Try to write that in words, maybe within two seconds and 40 characters. And would it be more clear, or less clear?
As subtitler you would have to consider a bunch of things (readability, CPS-ratio, line length, etc. - see above). But also, who is your audience? I would say six year old kids will not watch a video about programming (although some six year old kids are better in programming than a lot of adults). Or is it made for a bunch of super intelligent and highly educated Einsteins? I think Einstein would understand the symbol for infinity
I think the bottom-line is that there is no right or wrong, the subtitler should consider all these things and decide what is best.