Sure, you'll be able to partake in Doomsday Heist content in a few weeks or months, but everyone is enjoying this new content now and when you get there, everyone will be enjoying other major DLC released since. This issue is mainly present in players who cannot dedicate a lot of time to GTA Online, as luckily it's more than possible to outpace Rockstar's development cycle if you put the daily hours in and catch up in time.
Another issue is population migration within-game from content to content.
Most players jumping into the world of GTA Online today won't be able to try out approximately 80% of the game's numerous Adversary Modes unless they somehow organize teams with that specifically in mind. Basically no one plays the old Adversary Modes, ever. The only Modes with full teams are the ones with the double reward bonus going on at any given time, and a small handful of evergreens like Slasher.
The content is still there, it's absolutely accessible, except no one will be there to play with you, and a bunch of GTA Online's content is decidedly unfriendly towards solo players. Finding associates for some Further Adventures in Finance and Felony CEO work sure won't be easy this day and age, for example. If you want to work yourself through GTA Online's content in order, you'll need to get ready for some loneliness.
However, after being laden with four years of extra content GTA Online also does a ton of things right to maintain accessibility. We previously mentioned two factors — not changing existing content and allowing players to catch up in a reasonable amount of time — but there are other mechanics and trends baked into the game that help new players feel like they're not in too deep.
In order to solve the issue of the sensation of missing out, Rockstar peppers both their major releases and weekly mini DLCs with some cheap options. With each passing DLC, more and more ways to make money are made available in GTA Online, and once you're past your first big bump — starting heisting — you'll soon have enough cash to get into newer content like CEO work.
Even then, every big DLC has one or two sub GTA$ 500,000 vehicles, and cheap vehicles being added as weekly DLC are more frequent than the expensive ones. Occasionally, Adversary Modes are revitalized for a short while when an older Mode is selected for a weekly double reward promo, when the population shoots back up to healthy again so long as the event lasts.
Working your way through the GTA Online progression is also made easier from the aspect of having to buy less stuff that, over time, becomes out-dated, than the folks who have been playing since launch. In a bunch of fields, such as racing, what was the top performing vehicle two years ago is barely worth driving today. Incrementally buying every newest fastest car over the years ate up tons of money from veteran players, but new players won't need to retroactively buy all that — they only need the newest best car, significantly lowering the "price of being new".
You can also refer to our numerous guides regarding progression, money making, leveling up and a huge library of DLC-specific guides to blaze through old content and catch up with the rest of the community in no time at all. A bunch of seemingly time-consuming or difficult missions and activities have loopholes, glitches or masterfully developed methods to cut down on difficulty and duration, speeding up progress.
Rockstar has also given players two optional shortcuts — Shark Cards and item packs.
Shark Cards began their life as Maze Bank Cash Cards, and basically have been around since GTA Online. You pay real cash in exchange for varying amounts of in-game currency, allowing you to fast track your way to expensive goods. The item packs are more recent additions, however, and offer a better value in terms of GTA$ worth, while also saving you the trouble of sifting through the game's mindbogglingly huge vehicle library to find the good stuff. These pre-packaged item packs help you boost your GTA Online career in a quick and easy way, so long as you're willing to pay real money.
In essence, the answer to the question stated by the headline (in accordance with Betteridge's Law of Headlines, funnily enough) is 'no'. It's not too late for new players to dive into GTA Online. It may actually be the best time to dive in — huge amounts of content, a huge player base, bugs mostly worked out, no hackers. It's the golden age of the game, pretty much, and it's absolutely accessible to new players.