I think Monroe and Horford would fit miserably together.
No idea why you'd think that...I struggle to see a better fit.
Horford is mobile, defensively versatile protects the rim, and is predominantly a perimeter player on offense.
Monroe has size and is one of the better rebounders and post scorers is the NBA, and gets to the line.
Both are excellent passers and good locker room guys.
Perfect fit.