Personally, I never had an issue with my clown loaches out-competing smaller fish. for food. I've kept them with a bunch of other small bottom feeders like corydoras, kuhli loaches, etc...And I've also added small fish like dwarf rainbows a few years back, and currently harlequin rasboras that manage to steal food just fine.. It is also a lot safer for fish to be added to larger, established and stable tanks than to some newly set up quarantine, providing the established tank is not overstocked or filled with aggressive fish....
Generally, I'd be more worried about diseases and for that reason alone I'd quarantine, providing the quarantine has perfect water quality....Majority of issues with newly purchased fish is caused by the stress of the move, mini ammonia spikes due to the sudden bio-overload and general stress from bad water quality conditions. So it is a real bad idea to quarantine for the sake of quarantine, if one doesn't have a quarantine tank fully cycled and running, which tank can handle the added bioload at once....Water changes are really important for newly added fish...I'd do them daily or every other day for at least the first few weeks.
