Doyle berries are very good. For a long time we thought they were slightly smaller than the TC that I also grow (and of course later-setting berries are smaller), but last season they seemed just as large when picked in the same part of the season.
I am not one for hair-splitting on the subject of "flavor", which is mostly in the mouth of the consumer. If it looks like a blackberry and tastes like a blackberry, I call it a blackberry. If you close your eyes, you won't be able to tell the difference between a fully ripe Doyle and and an equally ripe Triple Crown. Having said that, I don't think a climate like San Diego is ideal for growing any blackberry.
I have small yard and want to grow a lot of plants, so have only two blackberry plants. One Triple Crown and just one plant of Doyle's blackberry. When I was buying Doyle's plant and read on their website about its productivity, I thought this is just a sale's pitch. I have two bushes next to each other in very similar conditions (sun ,irrigation, soil, etc). Doyle outperforms Triple Crown for me, they don't even come close. I collect a ~ one gallon of berries from Doyle's plant several times per week for approx 1 month now and it still has plenty of berries in different stage, should be several more weeks of harvest. Triple Crown berries are a little bigger, but the amount is not comparable, probably 3-4 times less or even more and they are almost over by now. They started at approx the same time.
I can't comment on taste of fresh berries, both are kind of sour to my taste. I use both varieties to prepare home preserves. Doyle's (and TC) both make wonderful Jams w/o pectin, just berries and sugar. Tastes absolutely delicious on ice cream or home cheese (like Fromagina Quark, tvorog, etc).