Does English Breakfast Tea equal Assam Tea?

I believe that 'English Breakfast Tea' is a very broad definition and doesn't refer to an exact blend; each manufacturer has their own version of it. I would say that English Breakfast Tea often includes Assam, but as your Wiki source suggests it also contains other teas. Therefore Assam is a separate tea.

In answer to your question, yes, you can use English Breakfast to prepare masala chai, but it will probably be better if you use assam or second-flush darjeeling. A more robust Chinese black provide a good flavor as well.

What is English Breakfast exactly?

English Breakfast is a blend of black teas which gives a richly colored liquor, full-bodied flavor, and relatively high caffeine level. Generally it is a blend of assam (for body, malty and darker earthy flavors), Kenyan black (for color), and Ceylon (citrusy & flowery notes, for richer, more complex flavor). Fancier English Breakfast may include a dash of other things, such as Chinese Keemun, which has body similar to assam, but a different flavor, with notes of fruit, pine, flowers, smoke and honey, and less malty flavors.

Note that original English Breakfast included a lot of keemun, rather than the assam that currently dominates.

The problem with cheap breakfast teas, supermarket pekoes and low end earl greys/chais is that many of them use the dust of tea processing and not the real leaves. Black teas can vary highly in quality from Ceylon (high grown), premium Assam and Darjeeling and Keemuns to Nilgiri and also other China blends (Yunnan, Souchongs) and Nepal blends. They can also come from a lot of other countries in Asia, Africa and South America. Any type of tea can produce anywhere from orthodox to dust in this classification.

Lots of blacks are sold as orthodox such as such as flowery tippy golden black teas. Others are crush-tear-curl. The teas marketed as breakfast teas should not be all classified as cheap because some premium loose leaf ones are good -although most of them in the store are made from blends of dust. It is not true that blended teas are always lower quality its just that the blends they sell consist of the mix of dusts. Lots of orthodox grade blacks said to be better teas.

Crush tear and curl (CTC) is a method of making tea particles rather than quality loose leaf tea leaves and CTC is used for the commercial tea bag industry.

Orthodox are fuller leaf although even if a broken grade are higher quality although some are full leaf these are often pricy.

Black tea comes in all the forms. CTC blacks are cheap although orthodox black ones can go for very high prices.

OK so to say that my answer was not relevant to the difference between English Breakfast and Assam the difference is this - Assam is a single type (India tea) that varies in quality from premium to lower grades. Ceylon teas and Keemuns and teas from Kenya do the same. It is likely that if you are in a general store the Assam/Ceylon/orthodox China/Africa blends are likely higher quality than Englilsh Breakfast so yes Id go for Assam over EB on average although it depends on the English Breakfast. If you buy a specialty loose blend of English Breakfast it might be a mix of higher quality leaves from the same tea types/locations. English breakfast is likely a mix of all those teas - they contain assam mixed with others named although they often mix the lower and not the higher grades of those teas. So on average - yes - Assam and Ceylon called teas are often higher quality although even amongst those there are variations. Its just that English Breakfast is often a name put on the box of mass market cheaper blended teas.

I happen to have a box of Twinnings English Breakfast Tea (as sold in the US), and the box states:

Master Blender's notes: smooth, flavourful, robust.

Colour: Brigh, Coppery-Red

Strength: 3 / 4

Steep time: 4 minutes (recommended)

English Breakfast is our most popular tea. To create this well-balanced blend, we carefully select the finest teas from five differegions, each with its own unique characteristics.

Tea from Kenya and Malawi provides the briskness and coppery-red colour while Assam gives full body and flavour. The robustness from these regions is complemented by softer and more subtle teas from China and Indonesia. The combination of these varieties yields a complex, full-bodied, lively cup of tea that is perfect any time of day.

The ingredients list has:

Fine Black Tea expertly selected from Kenya, Indonesia, Assam, Malawi and China

US Law says that ingredients have to be listed in decreasing order, so it seems like this English Breakfast tea is predominantly Kenyan though contains Assam.