First of all, it would be worthwhile to understand what people mean when they say “there is no content”. It almost never means that there literally is no content they haven’t completed, rather just that there is no content that they deem a worthwhile investment of their time to complete. Let’s put it this way:
- leveling is content, but it also isn’t for everyone. For some people, leveling is just the dead period before they can actually do content;
- pvp is content, but for someone that is utterly uninterested in pvp, it only ranges from something they ignore if there is nothing worthwhile to get from there that relates to their own playstyle, to something they consider a massive inconvenience and nuisance if that worthwhile something is there; the reverse is perfectly true for players exclusively interested in pvp;
- pet battles are not content for someone that isn’t interested in pet battles.
And so on. This goes for every feature in the game, and the typical player behavior really is that there is content that someone likes and content that they don’t like, and what exactly that content is varies from player to player. Players that do all the available content with joy are in point of fact extremely rare; I can say that I haven’t actually met anyone like that while actually playing, and my friends list ingame is in the hundreds, which is not to say that such a person doesn’t exist, but merely that it’s not a common occurrence.
Now, Legion and BfA did/do have content. In fact, compared to older expansions, there is more content than before. At the very least, world content and dungeon content have a longevity they never had before. By this, I mean just what I said earlier, that they provide rewards that are worthwhile for people with multiple playstyle preferences, ranging from people who genuinely enjoy world content to raiders to pvpers. In fact, their reward structure is so generous that they cannot be ignored by practically any player that is interested in any kind of midcore endgame without that player losing big for it. What the systems are that facilitate this - titanforging, random sockets, AP, essences, rng legendaries and whatnot - and whether or not those systems are fun or better systems could exist is an entirely separate discussion than the point of this thread. And thus, we get to the main point, which is the “worth” of playing an alt.
One of the cool things about any game with several different classes or races or factions or anything along those lines is that these provide replayability. They provide enough change from the initial experience to make picking one worthwhile, but on the other hand all the previously completed and obsolete content once more becomes available and something to look forward to do. Taking WoW as an example, if I played through the content as a healing priest, and then roll an alt rogue, I’ll be playing not only with a different set of buttons and a different flavor, but even an entirely different role, which could make at least the more enjoyable parts of all that content I already did seem quite fresh. This is the great thing about alts and multiple classes.
However, there is a caveat. Many people are oftentimes willing to go through some parts that have worthwhile rewards, and I did give some examples earlier, the first time around, even if they find those parts boring or a nuisance. Most people also understand that their alts are not going to be at quite the same level as their main - this is obvious since there won’t be as much time dedicated to them, they won’t have as much practice playing the alts, and so on. But many people also expect their alts to be able to get close enough to the level of their main too - one wouldn’t expect a mythic raider to be content to do normal and lfr on their alt, or a 2600 rated pvper to be content to play at 2000 rating on their alt, or an expert mythic plus dungeoneer to only do +6s to +10s on their alt, at least not for an extended period of time. The issue here is that while the first time around, those boring nuisances were probably bearable, when it comes to doing it all over again the second or third or even fourth time around, it really stops providing any kind of fun and the annoyance only exacerbates. But as I said earlier, these types of content award things that are simply too worthwhile to skip.
So instead of alts providing a refreshing experience, they end up being sources of more boredom and frustration, and this part is true for a lot of players. The game needs systems that enable alts to skip the boring chores or at least skip them in part (speed them up), and get close enough to the point where the main is so the content they can realistically perform in is that which provides fun for the player. Instead of doubling the lifespan of the content that players find boring and nothing but a chore, they should double the lifespan of the content the player actually likes playing. That is the way to make alts a healthy thing for the game. That is one of the reasons why catch up mechanics are a good thing (the other reason being that they facilitate access to the actual game for new and returning players).
I’ll end with an anecdotal example of my own preference in how to play the game. For the longest time, the content that brought me the most enjoyment in WoW has been PvP, and specifically rated Arenas. Back in MoP and WoD, it was perfectly possible to roll an alt, level it fairly fast and then get it ready for playing Arena at what I considered to be a reasonable level, all that in a matter of days. So whenever I would get bored of my main, I’d roll a new character and it would refresh my game experience. In Legion and in BfA, on the contrary - getting a hypothetical alt to a level I consider reasonable would require perhaps a month of dealing with what is to me unfun, boring and annoying content, needed otherwise to get the proper essences, the proper azerite parts, the proper neck level, the proper gear, even if not at the same itemlevel as the main but close enough to not feel that alt is too underpowered, which leads me to the reasonable consideration that rolling an alt is a waste of my time, which further leads to the conclusion that I wouldn’t roll an alt. This is how I suspect many players end up feeling stuck on one character, and furthermore that one character is stuck on one single spec (for various reasons, ranging from the investment in the spec specific artifact weapon in Legion to Azerite gear in BfA). It’s, I think, not hard to see how from this point one might jump from this situation to the conclusion that the game has “no content” or that the new patch brought too little to the table. It’s really because the easiest means of doubling that existing content is effectively disabled by (the lack of proper) game systems.