What you are saying is correct in principle: we are able to support greater loads isometrically than we are able to move concentrically. However, the degree of the difference is not as pronounced as you remember. Isometric strength is typically in the order of 10 per cent greater than concentric strength. That is, if we can bench press 100 kilograms (220 lbs) for a one-repetition maximum, we would likely be able to support around 110 kilograms (242 lbs) at the weakest range for a similar period of time. There is individual variation, of course, due to our genetics (relative dominance of distinct muscle fibres) and training, but the difference will be within that range.
So to rearrange our wording to the way that you presented it above, if you can pull 200 kilograms isometrically, that would be the equivalent of pulling with a ‘force’ of around 182 kilograms concentrically. Yes, there is a difference; no, it is not so great as we might think.
That still leaves the question of hypertrophy. Whilst it has been long established that isometric exercise stimulates hypertrophy, it has generally been observed that concentric exercise stimulates more than isometric exercise, and isometric exercise more than concentric exercise—the theory being that greater hypertrophy is a function of muscle fibre damage. Nevertheless, isometric exercise, and particularly maximal isometric loading (like you are performing) has been observed to stimulate significant hypertrophy.
In summary, therefore, pulling maximally, or even sub-maximally, against an immovable object should certainly stimulate significant strength development and hypertrophy, albeit somewhat less than we would expect with normal (concentric) lifting.
I hope that helps.