Well, I CAN get a board true on two sides without a jointer (using a sled with a planer is probably the easiest way on the face and tablesaw jigs for the sides), but getting it true to those reference sides without a planer is imho even harder (at least on the face sides; the edges I'd run through the tablesaw to true to width more often than the planer unless the board was fairly narrow).
If you setup properly for it using a sled to face joint isn't really all that onerous, I didn't have a jointer for years, and while I surely do enjoy the one I have now it certainly wouldn't be the first machine I'd replace if I was starting over. The various sled tricks (planer sleds for medium pieces, router jigs for really wide ones, etc..) are worth learning anyway for when you get a piece of wood to wide for your jointer Edge jointing is definitely faster with a jointer but only maybe twice as fast as many of the alternative techniques - many of which are (again just imho) somewhat more reliable until you get your jointer setup properly and learn how to use it (and at least some of them are most likely safer). When setup well and used properly jointers are pretty sweet, if they are off (tables misaligned or cutter head to high/low mostly) they can be a real exercise in frustration.
In order of larger power tools I'd have want to keep I think it would be: a good bandsaw, planer, tablesaw, and finally jointer (ignoring all the "smaller" stuff like the shaper, and the "unrelated" stuff like the lathe - <3 my lathe, etc.. ) - this is of course not the order I originally bought in (more like crappy tablesaw, ok planer, upgrade tablesaw + planer/jointer and finally bandsaw, I regret the years I spent without a bandsaw but it certainly won't get you straight/flat faces).
The underlying issue essentially boils down to the old time versus $$'s and space tradeoff. If you can afford a good planer and a good jointer by all means go ahead and get both. Do you NEED a jointer? I've seen lots of people doing work of a high quality without one that says you don't (and some who are adamant that it wouldn't really save them any real time at all based on how they work).