I've been using the Gladiator/Conquerer/Reaver (or new 433 posted above) for a few seasons now. What I've seen is that the game reacts to your dominance at starts deviating from attacking formations to 4141s almost solely. This isn't a problem usually if the quality of the team is poor, but vs. a quality side you concede too much possession with Gladiator/Conqueror. You need the extra man in midfield to not get countered hard.
What I do:
Poor - 6th-4th place using defensive formation (4141, 4231 or 3/5 atb), at HOME or AWAY
I'll start with Gladiator, but if I'm down on possession or not getting shots on target after 15 minutes I'll use Conqueror. If they look threatening on the counter I'll go 433, otherwise I'll stay on Conqueror.
Any Team using 442 or 433, HOME or AWAY
I'll start with Gladiator, but if I'm down on possession or not getting shots on target after 15 minutes I'll use 433. If I can't find a goal by 45 minutes, I'll use Conqueror.
Top Team using defensive formation, AWAY
I'll start with 433, then use Conqueror if losing or unable to find a goal if drawing isn't acceptable.
Top Team using defensive formation, HOME
I'll start with Gladiator, but if I'm down on possession or not getting shots on target after 15 minutes I'll use Conqueror. If they look threatening on the counter I'll go 433, otherwise I'll stay on Conqueror.
Summarized, at HOME the Gladiator -> Conqueror approach works very well after the league takes you seriously and plays a SUS formation for 90 minutes. AWAY, you can get caught on the counter luckily by poor teams or fairly consistently vs. the top teams. Having an extra man in midfield helps. I'm not a fan of Shield Wall so I prefer using a 433 instead for a 3 man central midfield.
When losing, I find it most effective to sub in a fresh LM/RM first, then a striker.