I had a different experience although I booked directly with the Sri Lanka Airlines. Sri Lanka Air's (SLA) business class fares are a good deal.
Usually business fares are 3x to 4x more than economy. Not so with SLA; my business fare CMB-BKK was $356, slightly double that of economy.
That gains you entry to the Serendib lounge at Colombo's Bandaranaike International Airport. While the lounge has seen better days, there'a good buffet and travelers are entitled to free showers and a 15-minute head massage. As I had a 7:50 am flight the lounge was not crowded.
While SLA has newer Airbus 330-300 with individualized seats in business class, this flight makes do with the older 330-200 with adjoining seats. I lucked out and had both seats to myself. The breakfast menu offered an extensive tea selection and several meal entrees.
What's nice is SLA's direct flight lands at Bangkok's Suvarnabhumi (BKK) airport with speedy rail service into the city. Air Asia, while offering the cheapest economy fare, needs a stop over in Kuala Lumpur and lands at Don Muang (DMK) airport - less convenient than BKK.
Given the near 4-hour flight, extensive breakfast selection, lounge access with free shower and spacious seating, it was well worth the business class fare.