As a fellow ancient of the game world, I would say 20ish years is not far off give or take. The Atari 2600 was around in the 70s and the original NES came out in 1985(?). The NES was really the beginning of the end for the arcade scene. True that a lot of the arcade ports where terrible, but the power just wasn’t there to do it in a small box yet. $1 rentals from the local video shop would let you play a game all night or longer depending on who it was from.
While the online game services from Xbox and co could be seen as returning to a pay-to-play situation, they where never a must have. You could still play with friends locally without a subscription and the mass push for DLC buys wasn’t there yet.
I would really put the return to money snatching along side the rise of mobile games. Buying addons and in game coins to get an advantage really picked up with the ease of always on connections and purchases with a simple swipe of the finger. Once that ‘just one more boost will do it’ addictive mechanic was made the norm it was all over for the concept of a game that you just bought as a complete thing. Now it’s a novel thing to see a game offered that you just buy and play as it is.
What is DLC vs an expansion has become somewhat blurry. There was StarCraft BroodWar that was really an entire separate game to the point of launching them separately at the menu. Now things like Rimworld (which I play far too much of) have these expansion/plugins that add new mechanics and features but don’t create a separate game in their own right.
I actually read an article recently about 20 years of Oblivion horse armor or some such. They made an interesting point that a lot of the acceptance of micro buys came from online games letting you show off your new gear to the masses.