That was intentional. I thought most platformers (even Super Mario Bros unless I'm mistaken) had variable jump heights depending on how long you hold down the jump key. I can only think of a handful of mostly older platformers off the top of my head that have pre-set jump heights such as Manic Miner.
And actually you'll need that variable jump height to get past some jumps that need high jumps and some that need low jumps (because of overhead spikes). It probably does make the game harder that way, though! And yeah, it's a tough game!
Although, I can't say whether or not my implementation is any good! It felt correct to me, but of course I was the one playing it everyday for a month and never had time for any real outside play testers!
