Yes, if you're reading French from the 12th century, or whenever that spelling was standardized, you might find it helpful to pronounce the letters as they were pronounced at that time.
And I say this as someone who is fascinated with historical pronunciations.
When reading Molière I actually use the XVIIth century France French pronounciation, so no problem. I use the I century b.C. pronounciation for Latin, so no problem, I also like historical pronounciations. The thing is I see quite a division in the Greek one, and particularly towards the Modern Greek one. Of course I'm not suggesting this should be the, say, official, or leading pronounciation, but I will rather use this one (I have no problem whatsoever in using the ancient/reconstructed/erasmian one, but it seems to me slower
English has nothing to do with it.
I said English because I presume a most people in this forum has English as mother tongue, nevertheless we use it as our κοινὴ when writing here. I just wanted to point out that there are also languages which have several spellings for the same sound (English for Spanish speakers can be quite a pain when writing, I can tell you). Ει, υ, οι, η would lead to no more different mistakes using Modern Greek pronounciation than ο, ω; or ε, η for someone who would not distinguish the length of vowels using the Ancient one.
“Captivæ Graeciæ lingua in paucorum Eruditorum memoria hodie vivit; laborandum est, ne omnino intereat linguarum pulcherrima” Balbinus, Verisimilia Humaniorum Disciplinarum, XII, 3.
“In omni disciplina infirma est artis præceptio sine summa adsiduitate exercitations” R. ad Herennium, III, 40.