Uh, FE:H definitely had more to do at release even if you just take in to account how long it took to level up characters compared to this game. FE:H certainly updated and added things quicker.
It did? My memory might be a little hazy, but I remember blowing through the main story content pretty quickly in FE:H (it didn't help that the story was pretty much a throw away, I really wasn't impressed with it :/). Inheritance wasn't even a thing then, so all we had to focus on after going through the ten or so chapters of the main scenario was grinding out our levels for the characters we had and do Arena every once in a while (or go through the main scenario again on a higher difficulty). It's more-or-less the same thing we're ding in F/GO right now, except instead of character levels we're farming ascension materials and/or XP cards to burn for Mana Prisms. If that's boring for you, there are A LOT of side-quests to go through for the first three areas of the game, not to mention all of the Interlude quests you'll unlock along the way.
Honestly the amount of content F/GO launched with was pretty decent. It might not have seemed like much, since the AP cap for completing the story quests were pretty much meaningless as we constantly had AP overflow meaning we could basically sit there and go through the whole thing without stopping. If we couldn't, like with FE:H when it launched and needing to wait for your stamina to replenish, it would have lasted a long time. The story was pretty lengthy too.
Content will come, but they're probably a bit hesitant to throw too much into the game right now since it could potentially be overwhelming to new players. Not everyone can play as hardcore as many of us are, so they're probably giving us a nice buffer between launch and the first "real" event, so people can level/ascend their characters a bit and increase their rank/team cost (hence the 1/2 AP promotion we have going on right now). The Gilgamesh event ends on the 20th, so I'm guessing in the next couple of days we'll hear more about the new event.
I've spent basically all of my quartz rolling for Gil, and while I've gotten some nice CEs like Limited/Zero Over, Formal Craft and Be Elegant as well as NP5ing FSN Cu Lancer and getting a Tamamo Cat, I still kinda feel bad. I guess I should still be satisfied that I rolled Waver as part of my tutorial quartz on the first try, and him and my free Herc can clear all of the content no problem. Gil is definitely one of my favourite characters though so it's a downer that I can't seem to roll him, as he's limited. I still have a little bit of quartz left to get in Rome and the remaining free summon tickets so fingers crossed, but I'm coming to terms with the fact that I probably won't get him. The only other banner that really interests me in the near future is the Okita one, and I don't have nearly the same want for her as I do for Gil. Oh well.
Don't worry, Gilgamesh will come back. Just start saving up your tickets/quartz again and try later. I believe he returned 3-4 times in the Japanese release, so this won't be your only shot at him.