The issue with Epic isn't as bad as people imply, but it's very real. They produced an incredibly shoddy launcher and store, frequently engage in anticompetitive practices like exclusives, and are happy to frequently update their launcher with new unhelpful bullshit without addressing its core problems.

Me, I'm not upset that Epic exists, even as a Steam user I would not like to deal with them as a true monopoly. But, they give me zero reason to use the store.

The problem is that it's a half-baked product.

I just don't use Epic myself but do use Gog and Steam (with the ultra shitty EA launcher and Ubisoft Connect bundled with some of my games) and Playnite has changed everything unifying it all into that single launcher.

Full screen mode in Playnite works fine on my HTPC and as a launcher it does consolidate all of them into one place easily. Worth trying if you use multiple stores.

As for why I'm not using Epic, the whole paying for exclusivity with third parties really didn't appeal to me at all.

If the free offerings from Epic do appeal to you, or if they do better deals on localised currencies (especially if you do struggle to pay for things), don't worry about using their services. I wouldn't want you to deny yourself some entertainment just because other people have issues with them as a business.

There needs to always be multiple game stores to keep prices in check. Steam can not be the only option or prices will skyrocket. See game console stores for reference. I use Playnite to seamlessly bridge my game libraries from Steam, GOG, Epic, Amazon Prime, itch.io etc. This is the way.

Just my personal opinion

The good clearly are the free games and that some games go cheaper there, they have better sales sometimes. The bad is that the store is badly optimized. The UI is annoying, no cloud saves for a lot of games. As of recently there were no achievements or even a cart, but they have that now which is good. The friends tab is bare bones still. They have aggressive DRM. For some reason it's a pain in the ass to log in, but that might be just on my end.

Now with GOG, you don't have DRM, you can integrate all launchers so you can launch all the games from one, which for me, is pretty useful. GOG has great deals. The bad is that the ui as well is kind of bare bones, but i don't know, they are not trying to take over the market and their store works very well.

As of steam i don't need to say anything, everything is in there. If you play on linux you basically will get every game from steam. They have the most robust launcher with the most options, etc.

That said, personally I use the three of them. Gog primarily since i can launch everything from there and if i find a game in there, i'd rather get it from them. But i've found sales on epic too good to let go so i play those games there. For me it depends on what they're offering, but for some reason i really dislike Epic's layout and ui, i feel like it is very annoying and that it is missing a lot.

what’s the issue with Epic

Enshittification.

why should I go for Steam

Not sure you should.

or GoG?

I hear GoG tends to be less DRM-y.