I would advise against relying on bots. Developing a good AI for a multiplayer game is a lot of work and players will still notice. I have seen some MMO games which started to use bots to reinforce teams when their playerbase started to decline (like Planetside 2), but this was usually considered a controversial move by their communities. Playing with other humans is the whole purpose of an MMO game, after all.
If you want to make sure that you have a large playerbase, then pre-launch marketing is important, especially for a multiplayer game where the size of the community directly impacts the game experience of the individual player.
If you "have been funded or invested to make huge game like that", then you should also assign a considerable part of these funds to your marketing budget.
I don't necessarily mean mass advertisement. Advertisement is great for AAA studios who got the budget to saturate the advertising space in order to make everyone and their grandma aware of their game launch. It is also great for the kind of game experience which wants to maintain a slow but steady influx of new players. But it's not really that great to get people hyped for a launch.
The best way to get people hyped is by building a fan community before your game is released.
- Create a community hub for your game where your community can interact with each other and with you. There are different opinions about how to create such a hub. Forums are the classical solution, but seem to fall out of fashion. Options which seem more popular right now are an own community on reddit ("subreddit") or a Discord server. Feed them regulary with small bits of information to keep them interested.
- Feed the gaming press with regular press releases.
- Get into contact with streamers on Twitch and let's players on YouTube and organize public tests with them.
- Announce your release long in advance. Not just the day, announce the exact time when the servers are open.
Promoting a game during the month leading up to release is a full-time job. If you are a solo developer, expect to spend more time on promoting than you spend on development during that time. When you are a small team, consider to hire someone who does nothing but promotion. Larger game companies usually have whole marketing departments.