If you don't do a proper presoak when processing film, you will get uneven development.
Not so. For many years Ilford specifically counselled against presoaks as doing more harm than good. Then, when they realized that people were going to do them anyway, and they didn't do any real harm, they stopped worrying.
Most of the developer is only there to wet the film quickly and evenly -- you don't need much to do the actual work.
Very short development TIMES are another matter, which is why a 5-minute minimum is normally recommended.
The best way to put the film in the dev is to have the tank open and ready, and lower the loaded reels/hangers into it as smartly as possible without splashing.
Consider also Polaroid peel-apart. Where is the presoak?
Throughout history, the vast majority of photographers have not used presoaks, not least because they are almost invariably completely unnecessary. I myself have never used them in 40 years.
Sorry to be a trifle aggressive, but this has always struck me as one of those things people do because they've always believed they need to, but have never actually investigated it; or because they're worried by advice to use pre-soaks, which they needn't be; or to demonstrate their superior knowledge, when they don't have any. We all acquire ritualistic habits, but this one is a waste of time and water -- unless, as PE says, you're tempering at the same time.
Cheers,
R.