for sure there is a learning curve with a lightweight fiskars or other light weight axe, over the muscle memory of decades of monster maul splitting. I only swung one of those a few times, I am just not built big enough to deal with one. I mean I am down to under 120lbs in my neogeezerhood now..I have to work more efficiently, I can't just burn young guy energy or work with older big guy with bulk and strength type status.
My regular el cheapo 8lb is about as heavy as I would want to swing. I am an aim small hit small kinda guy anyway. Fiskars works for me within its design parameters, accuracy and focus and reading the wood and fast decision, keep splitting, or set round aside until later, using plan B or C. And I split inside a tire, helps eliminate any possible overswing type problems. Bounces or trying to split what I call rubber wood..I don't until it has dried more in the round. I will shave off the bark to speed that up.
If I am not noodling (easier) and just want to crack something the fiskars won't do easy, I just slam my 8lb maul into the round where it needs to be and drive it home with the sledge if that is what it takes. That works pretty fast. If needed at the same time, I will add some wedges. just depends..
*mostly* once a nasty crotch piece, etc, is whittled down to fit in my heater I stop there, I use those uglies for all nighters. The top on my heater swings up and you can set in quite a large chunk, say a 12 inch diameter or thick by 16 long, will drop right in there..
Also, by taking a lot more small rounds/ branch wood than most guys, I eliminate having to split as much, it is cut and stack then.