Describing something that was the best solution in its time

The phrase state of the art covers what you describe:

The term "state of the art" refers to the highest level of general development, as of a device, technique, or scientific field achieved at a particular time.
_Wikipedia

So you could say:

That was state of the art a decade ago, but much better techniques are available today.

If a better solution is now in use, the older one is outmoded and has been superseded, meaning that it's been replaced by something both more recent and (by some measure) superior. The implication is that the old way might well have been the best thing available at the time.

If there is not yet a better solution, but you want to show that the current one has flaws which weren't previously apparent, I'd consider something that stresses its age, for example archaic, hoary or timeworn.