The problem with your theory is that Goku get exponentially stronger. So let's say
x represents Goku at the start of DBZ. For argument's sake, this is how his power progresses
- Goku vs Vegeta. Goku becomes
x^2 during the fight
- Goku vs Freeza. Goku becomes
x^4 during the fight
- Goku vs Cell. Goku becomes
x^8 during the fight
DBZ is an over-the-top fighting series. Goku uses this to train before Freeza (#2). He struggles greatly, especially when the storm in space causes the system to malfunction. He ultimately defeats Freeza so it's safe to say he's much stronger by the end of the arc. That's the only time we see him struggle with it. But we have a solid benchmark here. Trunks handily defeats a rebuilt Freeza, but loses to Cell. Goku loses to Cell as well, but he's definitely stronger by the end.
It's pretty safe to say that Cell(final form) would probably laugh it off. As such it would be moot to try from that point on in the series.
Dragonball Super more or less confirms this. We see Goku unable to move when the gravity machine goes to 100 in DBZ, but in this clip from DBS, we see Vegeta moving freely in 150.
The DB Wikia page also notes
In the Trunks Saga, an upgraded version of the machine is created to help train Vegeta. According to the Daizenshuu, this more powerful version can go up to 300 times Earth's gravity. It is destroyed in the same Saga, during training. However it is subsequently rebuilt and Vegeta later increases the forces to over 400 times Earths gravity.