These are regular fares for SIN - DMK - SIN, with the former being slightly more expensive.
I've been taking SL since last year, as DMK is 30 min. from town vs 1 hour for BKK with no traffic.
Don't need lounge access or food on such a short flight, and there are plenty of F&B options at DMK ( as well as several 7-11 and Starbucks etc.)
Everything works as it should be, or as well as it can in Thailand.
Once in a while, you get awesome ground staff & cabin crew but you should not be expecting any smiles or extra service.
It is good, for what it is and nothing more.
p/s LION offers 20kg checked baggage with every ticket, even if the OTA says none is included. Air Asia offers no free checked baggage.