People that claim to disagree while pointing out examples of games that have both "comedy" and "serious" moments are kind of off the mark. You can absolutely have both. They are two sides of the same coin.
Edgar Wright's movies are usually perfect examples of this and what I point to most of the time. Shaun of the Dead is one of the funniest movies ever made. It also features one of the most heartbreaking scenes in any movie where the protagonist is tearfully forced to kill his own mom. Hot Fuzz is also consistently a laughing riot until one of the characters needs to deal with their dad being the antagonist. The World's End
which features one of Simon Pegg's most hilarious roles as a perpetually drunk and obnoxious goof who never left his teenage years, having to deal with an alien invasion after forcing his friends into a pub crawl, ends with this emotional gutwrangler of a scene.
All of this still holds a consistent tone despite a scale that constantly evolves. You can have an inconsistent tone even if you just focus on telling a story without comedy or without serious moments, but if you want an example of what an inconsistent tone is with elements that feature both, Star Wars Episode III is a good example. We go from Anakin committing a Jedi taboo in the opening scene that dramatically alters his character, and a couple of minutes later, we're back to Obi-Wan quipping and R2-D2 doing stupid slapstick shit. Then in a later scene, Obi-Wan is back to quipping while Anakin brutally slaughters children and gets burned to a crisp.
So yeah, when you point out that a game goes from having serious moments to slapstick comedy, keep that in mind. I'd argue something like Persona balances this stuff well because it's essentially a story about high schoolers thrust into world-ending scenarios; the humor is primarily brought about by character and the fact that these adolescents are still viewing the world in a very casual manner. It's also a very long story that spans an entire year of character-defining experiences where they all experience growth, suffer loss, have fun etc. However I will point out that Persona 4 does this element much better than Persona 5. The former generally keeps things balanced in regards to what characters experience but the latter flubs the transition between chapter 1 and 2 pretty exponentially and how it deals with Ann.
In regards to Metal Gear Solid, I actually think tone is one of the main reasons the series has preserved and also why everything post-MGS3 has been met with divisive fan backlash. The original titles were very much informed by campy spy epics, with the first two in particular leaning heavily into it's own self-aware, over the top surrealism. The key word of these games' tone was "camp". That persisted throughout the first three MGS games, but was eventually lost after the subsequent game doubled down on it's morose and miserable tone, which was where the tonal issues became far more obvious.
Super Bunnyhop has a 40 minute long video on MGS3 and why it's mixture of camp and tragic overtones is so well executed, and is part of the reason why it in retrospect is commonly thought of by fans as the masterpiece of the series.
