How can I counteract the to bright tomato taste of a beef stew?
The thing to avoid with stews is boiling them as this tends to make the meat tough and drives off the more subtle aromatic flavours, cooking too hard can also make tomatoes taste a bit metallic. 

If it tastes a bit too sharp there are a few this you can do to help it. 


seasoning : just basic salt and pepper flavours will help as well as plain salt anchovies and fish sauce can work well with beef, if used moderately  these don't give the dish any sort of fishy taste. These also tend to enhance the savoury flavour of the beef but you do need to be a bit careful not to over-salt stews as this is difficult to fix. 
sweetening : a bit of sweetener can counteract harsh flavours and enhance aromats. Something like honey or caramelised onions is generally better than refined white sugar, black treacle also works well with beef as it has a bit of bitterness to balance the sweetness. 
Spice : even if you don't like hot food, paprika or black pepper can add extra depth to a stew without making it too hot as can fresh peppers. Aniseed flavours like tarragon, star anise and fennel seed also work  well with beef. 


Smokey flavours can also work well and can be a good emergency fix for a stew which has gone a bit wrong eg smoked paprika or smoked oysters. 

The key thing is to add seasonings gradually and taste as you go along, taking careful note of how they change the flavour often it sis not so much a case of tasting the seasoning itself as how it changes the whole balance. 

Also stews get better with slow gentle cooking (not boiling) it's normal for a meat stew to taste bit weird after 30 minutes or so but after 45 minutes to an hour of gentle simmering is should start to come together so it's important not to season too much too early.