For me, the beauty of tai chi chuan lies in one person weaving through a group of others: they may be people in a crowd. They may be training partners. They may be dedicated assailants.
It seems to me that the "stand-up fight" is a rare thing nowadays, the one-on-one duel, if it ever existed, now seems a thing of the past.
There's a line in the Classics which never sat right with me: "How can an old man withstand the attack of a group of youths?" Our response for a long time was: "He bloody well can't." After a real-life encounter with the hitherto mythical group of youths, the classics didn't seem quite so silly. Perhaps an unfit man of seventy or eighy years of age would be unlikely to withstand such an assault; but a slightly younger, relatively fit and trained individual? Maybe he or she would stand a chance. Notice that the claim was only that the old man would "withstand" the attack. Not trounce, or beat the attackers to a pulp. Merely survive.
Tai chi chuan is difficult to categorise as a martial art. Its strength lies not in competition sparring, nor particularly in striking, and definitely not in kicking. It contains no groundwork. It is a civilian, family art so it had no place on the battlefield. In the eyes of many martial artists, I'm sure this seems to add up to a flawed art. But imagine one person against a small group, and sudddenly it begins to make sense. The emphasis on flow becomes pertinent, because to halt and fix in place in order to deal with a single assailant lays you open to attacks from the others. The same reason deals with the lack of groundwork, although escapes from ground positions I think would be really useful, and are not included within tai chi chuan as such. The emphasis on destroying balance rather than doing damage per se makes sense: it's quicker and allows of more movement than does standing toe-to-toe and knocking lumps off an opponent. If you can strike as you move, well that seems to work just fine, and fits with the tai chi notion of punching like a ball on the end of a chain. Try it for yourself.