Originally posted by micromacro OP has difficult time to stay loyal to Pentax because he thinks that other systems produce better results.
As a user of multiple systems myself : Canon,Nikon,Pentax, Leica - if you equip them with normal lenses, they will produce essentially the same result*
What really matters is what you do with the equipment you have. Compared to Pentax: It is easier to get new equipment if you shoot Nikon or Canon, as camera stores are more likely to have their lenses and accessories in stock. Brand loyalty in commercial photography is pretty pointless IMO, you have to use what will get the job done: and there are some specialized lenses that some manufacturers have that others do not - The Canon 24mm T/S-E and 17mm T/S-E , But Nikon have better super telephoto lenses and superior tracking AF systems to use them with etc,etc, so on and so forth.
For the most part I get clients that ask for a very specific kind of image where only a particular lens or camera will be able to give me the result that will have the qualities that will satisfy the client**. But those kind of requests are pretty uncommon, I have used my Pentax APS-C and Leica RF cameras among Canon and Nikon cameras for commercial work and my clients were none the wiser. Amusingly, there have been some instances where a Client blindly chose the images from the Leica or Pentax cameras rather than the more mainstream Canon or Nikon cameras. I suspect the culprits for this phenomenon is that both Leica and Pentax produce lenses that have interesting rendering characteristics than the offerings from Canon or Nikon.
Pentax K5IIs - Sigma 18-35mm f/1.8 ART @18mm f/1.8 ISO 80 1/640th
*Except for the Leica S2 and 645Z, Canon and Nikon Full frame DSLRs don't hold a candle to those two cameras.
** my personal preferences have no place here, Some lenses produce very particular "looks" the output from the Pentax FA*85mm f/1.4 is superior to the Canon EF85mm f/1.2L, which is different again from the Leica APO-Elmar-S 180mm f/3.5.