Vanguard has a lot more rules interactions and it has a lot less rules templating.
Like, look at how Knocked-Down affects everything, and can do so in a bajillion ways: movement, engagement, outnumbering, attack rolls, armor, line-of-sight, casualty removal, retaliation, fallback…
Depending on how the model gets Knocked-Down it may or may not be fatigued. Knock-Downs may result from getting 3+ hits or getting 1+ hits or getting 1+ wounds or a Speed test or a Nerve test. It can sometimes be cancelled on a bonus roll or a Nerve test or automatically with Power or by units just outright immune to it. It can prevent some friendly spells from targeting the model or some abilities being used by the model. It prevents any movement except when it doesn’t…
Whew! And that’s just rules related to Knocked-Down! Multiply that by every other mechanic and it’s a beast. And every time you face a new faction, you are potentially having to learn a bunch of new interactions.
All of that is fine - Vanguard is all about flavorful individual action which lends itself to simulation, a game where people can be bowled over by charging cavalry or overwhelmed by nightmarish terror, and those experiences should feel different. But it does take a game with relatively simple core mechanics and creates something a bit complex and fiddly.
If I had a time machine, I would go back a lobby for the Vanguard engine to be more templated.
I think a lot of rules interactions like Knocked-Down could be tightened up, all the different rules that have 2" or 3" ranges could be merged into 3", etc. Cans/can’ts of Engaged/Activated/Fatigued can be simplified, etc. Heck, there’s even an argument for removing Fatigue entirely and just using a single type of action currency.