I had given my brother in law some chilli seedlings earlier this year, which he grew outside in his south coast garden, producing chillies that he described as lukewarm- he was eating them when he walked past the plant.
I grew mine on a west facing Bedfordshire windowsill and having an excess of fruit passed some on to said brother in law. He proceeded tool one in his mouth dispute my words of caution as to their heat and had to run for a glass of milk.
I would therefore suggest that flavour may be down to heat, watering or feeding rather than seed?