TMNT for the NES was a very hard game, and I was never able beat it. I owned this cartridge and played it beginning at age 6, I think. I probably lost at the infamous dam level 5 or 6 times, forcing me to try again, until I learned the path to take to find each bomb, and then never lost on this stage again.
I played the dam level last night for the first time in over 20 years (thanks to The Cowabunga Collection), and beat it on my first try, with all four turtles still intact. Just as easy as I remember it. I have no idea why the difficulty of this level is always mentioned in the same breath as Battletoads, Ghost n’ Goblins, Silver Surfer, etc. The game was plenty tough, but the dam level was absolutely not a major contributing factor to the difficulty.
It’s pretty doable. You already mentioned some other games too.
But that little sewer jump took me way too long to get right consistently.