I frequently use the water displacement method to seal ziploc freezer bags when I sous vide. I can get maybe 99% of the air out, but technically the bag is not under vacuum. If I clip the top of the bag to the side of my container, any air pockets that emerge collects at the top, and the meat is entirely in contact with the bag and immersion bath. Alternatively, if I seal the bag with a marinade, there are no pockets of air between the meat and the immersion bath.   I can't imagine that the temperature transfer can be any more effective when vacuum sealed. So why does a site like SeriousEats still suggest that a vacuum sealer is needed for best results with longer cooking times?    update from http://www.seriouseats.com/2016/08/how-to-seal-food-airtight-without-vacuum-sealer-water-displacement-method.html#comments-299859  In the context of food storage in plastic bags, SeriousEats claims, "excess air causes oxidation that can develop into off flavors or promote spoilage." But I never sous vide for the freezer, it gets served when done.   There was a comment that asked if food contamination might occur for cooking times longer than 48 hours, but it was never answered.   What is the science behind this statement? How much residual air is "too much"?   If the bag remains submerged, does not leak, and the food in full contact with the water bath, is that enough to duplicate the benefits of a true vacuum seal?  update 2  Also, what is the scientific impact of trapping small amounts of residual air in a pocket above the water bath?  This assumes that there is still a very strong thermal coupling between the water bath and sous vide item.   In the photo below, you can see at least a 2inch gap between the air pockets above water level and the actual short ribs. From a heat transfer perspective, I can't imagine that a vacuum sealed bag can perform significantly better—certainly not relative to a 48hr cook time. Is there a possibility of bacterial contamination?    
This is a great question, but not one that can be answered with "yes" or "no".   In some areas, it is known that the professional grade tools and ingredients require much skill to use well and so the general public is better off using consumer grade tools. (Try tasking the average office drone to create a report with Word or QuarkXpress and you'll see what I mean). But there is no such general rule in cooking. And yet, this does not mean that better quality meat will always make better quality food. It depends on the details of each situation.   First, what does "high quality meat" mean? A filet mignon is a prized cut, and costs much more than shank. But even the best cook cannot make a good stew out of filet mignon. So in the first place, you have to know which category of meat is suited for the dish you are making. Only within a given category will better meat produce better results.   Second, "quality" means different things to different people. A cooking beginner usually cannot recognize which meat will produce better results in the given category and goes by factors like price and store reputation to decide which meat must be better quality. This is not necessarily correlated to better taste. So, as a beginner, you can pick meat you believe to be better, but end up with worse results.   The combination of these two points means that you should be aware of the difference between a "better" cut and a higher-quality version of the same cut. A "better" cut is actually a different cut, so it's a substitution that usually won't guarantee a better result. But a higher-quality upgrade of the same cut is likely to make a dish better. So, you need the cooking skill to tell a given piece of meat will be a good substitution for your earlier choice (a higher-quality version) or not (it is simply a better cut). Also, if somebody is trying to sell you a different version, you need to be able to recognize its quality (marbling in steaks, color intensity in pork chops, etc.)  Third, you can certainly find many cases where the more refined dishes, which need rarer, prized cuts, require a lot of skill to pull off well. So, if you decide to buy the "better" meat - as in the filet mignon vs. shank example - and have enough knowledge to match the dish to it, your skill might not be sufficient to pull off the dish for that meat well, while it would have been sufficient to make a good dish of the type for which the cheaper meat was suited.   Fourth, for each dish, the relative influence of skill vs. ingredient quality will be different for the final dish quality. So, it is possible that for going from "horrible" to "kinda edible" you need to get some skill, no matter what meat you use, but the jump from "kinda edible" to "not that bad" requires better meat, not better skill.   It is impossible to list all possible situations, dishes and meat cuts and say for each where the end result quality is skill-limited and where it is ingredient-limited. I am afraid that you have to be an intermediate cook before you can recognize if a mediocre cook can improve his results by cooking a given dish with better ingredients.  