I never thought the Turbo Tunnel was that bad. In 3rd grade I got past it in a rental. The real thing is, Battletoads plays like the 3rd level from some degree on every subsequent level. You have to learn a little bit more of the next level before dying, then a little bit more on the next life. If you want to beat the game legitimately, you have to put in the time to memorize what you do at what point. The level that gave me the most grief was the second to last when you're riding the "Clinger Winger" bike things and have to press the direction that you're trying to go.
Either way, beating Battletoads reminds me of beating a shooter. There's a lot to learn and to react to and then once you've learned it all, you still have to not mess up but it's totally beatable.