1) Rotom may have higher natural bulk, but with Incineroar's defensive moveset and Intimidate, it is Incineroar is the better defense/support Pokemon.
2) Rotom is far superior offensively because if you run Incineroar, you almost always have to run a defensive set with Fake Out and Parting Shot. Rotom also has the better offensive typing and access to Nasty Plot to boost it's Special Attack and deal a lot of damage. It is also the better Pokemon for Dynamax as both of it's STAB Max Moves help it deal even more damage.
Bulky Support Incineroar
Incineroar @ Sitrus Berry
Ability: Intimidate
Level: 50
EVs: 252 HP / 4 Def / 252 SpD
Relaxed Nature/Sassy Nature
- Burning Jealousy/Flare Blitz
- Snarl/Protect/Throat Chop/Scorching Sands
- Parting Shot
- Fake Out
Run Relaxed Nature if you want Incineroar to be bulky on both sides or sassy for a more specially bulky set. You could use Flare Blitz, but since Max Moves like Max Airstream is so common, Burning Jealously gets you a free burn which can cripple physical sweepers like Cinderace and Rillaboom. If you do decide to run Flare Blitz, run Scorching Sands to have a good chance of a burn. Snarl for the Special attack drop, Throat Chop to disable Hyper Voice spammers like Sylveon and Primarina or protect is personal preference. I prefer Snarl for the guaranteed Special Attack drop that can cripple special sweepers.
Special Sweeping Rotom-H
Rotom-Heat @ White Herb/Life Orb
Ability: Levitate
Level: 50
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Overheat
- Thunderbolt/Rising Voltage
- Nasty Plot
- Protect/Volt Switch
This is a standard special sweeping set. If you run a consistent Electric Terrain setter (Pincurchin) Use Rising Voltage for more damage in the terrain. Volt Switch is always a good option to gain or keep momentum. White Herb can be used if you have a Life Orb on something else and if you want to nullify the first Overheat stat drop. There really is not a better Pokemon since they are two different play styles, stats, moves, and abilities.