You mean "far deeper than it was in the first game" then.
Because research was actually super simplistic in the first game, there was hardly any of it that was necessary to complete the game, and the research trees were short and shallow.
90% of the available research was only for fluff reasons, it had no impact on the gameplay, it wasn't game depth, it was setting.
Except I'm actually not guessing, I'm basing this on discussing the game with a variety of people, on numerous lets plays of the game, and on the discussions and information at the UFO wiki.I have no clue how most people played the original. I'm fairly certain you don't either - you're guessing, based on your own experience. If I did the same, I'd claim that it never occurred to anyone to try and avoid ground missions.
Now, not everyone skips late game tactical missions, but anyone who thinks about it for a few minutes will agree that they're actually not strategically relevant or rewarding, and will start to wonder why they didn't skip them before.