How can I make onion tomato paste taste more punchy?
A. To make the flavor of tomatoes stronger in a sauce: 


start with better-tasting tomatoes. Depending on time of year these will often be canned. There are many reviews of canned tomatoes, so I'll not
pass judgment here but there are some excellent ones out there. 
reduce the sauce more to intensify the flavor. 
Tomatoes are an umami flavor. Adding another umami to it could intensify the flavor you're looking for (such as marmite, anchovies, etc.). 
if you want to get really fancy you can try playing around with a centrifuge such as a Spinzall. 


B. To make onions and garlic stronger you can try combining sweated fresh onions and garlic with powder. Be sure to activate the powder in water before cooking directly in fat or the flavor enzyme will be
deactivated before it can go to work.