No matter what ratios are inside the box, all gearboxes of this design have one common ratio. Namely the final drive is 1:1 as in top gear the input mainshaft simply locks to the sleeve gear carrying the gearbox sprocket.
By "useless" you mean first gear is too tall for a non clutch burning, easy getaway?
I reckon someone has sold you a myth. Probably someone with the biggest crank sprocket money can buy. If anything, a T2 close ratio box would give a more pleasant ride, without the more pronounced differences in ratios of the intermediate gears of the standard box. Easy to change the crankshaft primary gear, gearbox sprocket and rear sprocket to get the ride that suits you, whether you want acceleration, easy cruising, high top speed or economy. A change here from standard of the original gearbox and rear sprocket will mean the speedo will not be 100% accurate if driven from the box, because the speedo is chosen by the calculated number of turns of the rear wheel per mile, not from the actual number of turns. Changing gearbox or rear sprocket changes this calculated value. Changing the engine sprocket alone does not affect the speedo, but alters the overall engine speed for a given road speed. Changing this engine sprocket involves less work than changing an already installed gearbox sprocket
You may find that inside there are just standard gears, but you have the needle roller layshaft and mainshaft.
A box with a needle roller supported layshaft is also likely to be smoother and quieter than one with a layshaft running on worn plain bushes. If it is what it says on the tin, you are indeed a lucky man.
Swarfy.