Well, consider the real use cases. When a spammable improvement is
barely better than everything else it replaces, you barely get any additional benefit. This is the case with Timar - its total benefit is quite limited. You get one

per farm it replaces, and that's with an additional investment into a building you might not otherwise need. Compare Poland, where you get +1
and +1

per farm replaced - so you'd need twice as many Timars per city to get to the same marginal benefit (if we consider all yields as equal in value). And that's not considering that for full benefit, you'd need to run a civic that might not be optimal in many situations (whereas you're also not considering the likely scenario that at the time you'd be running Serfdom, so another +1

to farms). It's ok in that it provides a bit of everything, but its marginal benefits are relatively low compared to most other NIs.