To me it seemed like JM1 required more strategy. The limit of 4 boosts required you to find the best places to boost. You couldn't spam them like in 2 and 3. Also, since the game only supports digital controls you could refine your steering alot better. It's not as easy to tap a analog stick. Those you tend to hold down till you get approximately where you wanna go. I remember one time I got so good at JM1 I managed to wipe out, but kept my bike going over a hill and I bounced the bike off another players head a few times. Also, d-pad was good to avoid obstacles and you need to be careful in levels with lots of objects. Holding down a analog stick wouldn't cut it on JM1 tracks.
I always used the D-Pad for ANY Jet Moto game, even JM2124. I just don't think the analog stick is good enough to do all the crazy fast movements you have to do. And yeah, JM1 required you to think about when you should use your boosts, but I find that more limited than anything. Also, JM1's physics are atrocious compared to any later installment of the franchise, like how you can hit something full speed head on and not crash, yet sometimes you crash by barely scratching the side of a wall, it's very buggy and random. Also, sometimes the bike just gets completely fucked up and you lose control of it only to crash for no reason.
Well, I use the analog stick in the later games cause that's how I played back in the day. When analog pads were new it's all I wanted to use cause they were supposed to be superior. Now I see that dpad is good for many games tho. I'm glad Castlevania SOTN didnt support the analog stick. Rumble would have been nice tho.