In the field, without instrumentation, it's the best we got. Furthermore at your power level, it doesn't need to be dead-nuts accurate . We just need to the nearest 200 rpm, to be able to differentiate what you might have. It tells us a little about the efficiency of your engine, and why it's not burning up the tires, and helps to predict where it needs to go, if you up-size the cam.
It's like this; a given TC will stall differently depending on the input torque, and the output load. In a given chassis; You can take say a 904 TC from a slanty and put it on a stock 318, and it might stall 300 to 400 rpm higher. And then bolt it onto a stock 360 and see the stall rise another 200, and then onto a 340, and see it drop back to the 318 level. If you were familiar with the TC, you could tell by the stall,what engine was in front of it without ever opening the hood.
The TC is a key to unlocking off-the-line performance, because it lets the engine spool up to an rpm where the power is that you are needing to make it accelerate from a standing start, at the rate you want it to.
You can line up several TCs with a stall difference of 300 between each, and watch your take off go from; worn out nag, to hard working Betsy, to quarter-horse, to stallion, to Thoroughbred racer, with each change in TC; without ever touching the engine.
All a 318 needs is a 2800 to make it feel 40hp bigger. Then swap out the 2.73s for 3.91s and Hang on Harvey! It's like a mini supercharger.