It's absolutely relevant. Sometimes junior debt trades a little bit like equity but the point is that bonds mature whereas equity exists for the lifetime of a company.
>... price is what actually matters when it comes to securities like this.
Absolute return is what matters, not price. The return of a bond - junk or otherwise - is known on day one of a bond issuance in the absence of default. That makes fixed income a fundamentally different asset class to equity.
Even a junior perpetual junk bond is different to equity. The junk bond's coupons would be fixed, whereas dividends vary according to company profits.
For literally everyone else, it is, in fact, price that matters.
I made the distinction between price and total return above because an asset's price can remain more or less constant while still being a profitable investment: for example a utility company with a high dividend yield.
Let me try another tack. Would you rather own non-voting equity or junior debt in a company that is about to strike a deal that will make them wildly profitable?
"Fixed return" isn't really relevant from a practical standpoint because shares and junk debt both have volatile prices, and price is what actually matters when it comes to securities like this.