From what I have seen here, I don't think I have ever seen a negative remark about a Gretsch, That cannot be said about Epiphone guitars in general.
What is your own personal observation from checking out multiple examples of both companies? Or do you just go by what you read on the internet "in general" about Epiphone and "around here" about Gretsch?
You generalized opinions you've read online, but can you share your first hand experience comparing them? I've spent quite a bit of time in the semi-hollow room at Long & McQuade on Bloor St. doing just that. I don't claim to be an expert, but holding the guitars in my hands and playing them side by side, even with my limited knowledge, I can see the similarities and differences.
I've found the lower-end Gretsch Streamliner guitars that I've seen in similar price brackets to Epiphones (let's say, the Casino, Dot and Sheraton between about $500-$750) at the same level of quality, construction and finishing. In fact, comparing those head to head, I preferred the Epiphones over the Gretsch offerings. Epiphone makes some lower-cost, lower-quality entry-level guitars, but once you get into the $500-$750 range, they hold up well in comparisons to Gretsch in similar price points. Gretsch definitely has a good thing going in the MIK Electromatic hollowbody lineup, but those are usually above $1K. When you're talking Electromatic, I'd pick the Gretsch over the Epiphone. Of course, at that price point you're paying about $500 extra, so you'd hope to get a bit more for your money. The Electromatic lineup are a homerun for Gretsch, I think, as they have a great balance of quality to value for money and they look and sound great. I've had some serious GAS for a G5420T or the G5422T.
Also, if you look at the Epiphone "packages" or "signatures" in around the $1000-$1200 range, where you often get Gibson pickups and a nice hard case included, they are very good guitars at that price (eg. the 1955 Les Paul Custom Package, which I was very close to buying). At the high end of Gretsch their guitars compare favourably with just about anything I've seen, but you're into multiple thousands of dollars.