The truth is that sweet &sour sauce is WHAT YOU MAKE IT.
A good standard recipe is to start off with: 1 tab sugar and one tab of red wine vinegar, 1 tab of cornflour thickening and one tab of soy sauce (first tab thick/dark any later, light), plus your RED FOOD COLOURING, a small dash to give it that deep colour.
Then:
my normal:
Cantonese style: use fresh pineapple, green pepper, carrot rounds, onion quarters, and of course pineapple. Dilute with orange juice.
OR:
Chinese vinegar, sugar, cornflour, preserved vegetable (canned), Sezchuan preserved vegetable, some fresh fruit del la saison, bean curd cheese, and a bit of what you fancy. You can add some chilis also if it is not hot enough.
Experiment.
If you want swet & sour, then do that.
Hot&salty, do that.
Tomato, is NOT normally a constituent of a sweet or hot sour sauce, except in the west.