Yeah I would say a theme edit could possibly be a fix for the dupe title thing. Do you have more specific examples? Really need more context.
The duplicate tags seem to have been removed once I deleted the SEO app but I believe Shopify is adding the additional text at the end of our SEO title tags to include “- Crazy Critters” which I’d prefer to remove if we can. This is an issue we can address anytime though, I’m not in any real hurry.
For example, if one title tag was " Reptile Food | Large Live Crickets" the other tag was " Reptile Food | Large Live Crickets - Crazy Critters “. They were exactly the same, just one tag would have
" - Crazy Critters” added to the end. I believe this is Shopify, but I could be wrong… it’s been known to happen from time to time 
especially with things I know little about!
The Shopify Admin UI has a number of limitations and the SEO title/meta fields are one. Wrong lengths, no rule based logic exposed within the UI etc. So kinda just need to understand the limits. 3rd party apps (as you’ve discovered) are one workaround to viewing the “full”
My understanding of SEO is very basic. I didn’t realise you could use pattern/logic within the website code but this makes sense now that you have said it.
I suppose this is why we would definitely need to hire someone to address SEO in the future lol.
We’d probably just get a review of our SEO and work off any recommendations. I don’t know enough about SEO to put-forward my own suggestions on how to address it.