It can be a good everyday card for someone with the right spend. If you buy a lot of plane tickets or eat out a lot, the PRG is great. I prefer the CSP since my restaurant spend is high and my travel spend is not purely for air travel. Both restaurant and travel categories combined are about 50% of my overall CC spend. If I swapped to the PRG, I would need another general travel card since the PRG is much more narrow for travel.
As you indicated yourself, you cannot maximize benefits with one card. However, if you want to use only 1 card and get decent benefits, you need to take a close look at your spend. Next, you need to value points from various programs. Finally, you need to figure out which card gives you optimal overall rewards for your spend. I use 5 cards on a regular basis to optimize my spend and a 6th floater sign-up bonus card when I have one. If I had to pick just one, I would go with the CSP since I value its points at over 2 CPP, and thus even a 1 point category beats a 2% cash back card. Moreover, a sizeable portion of my spend is on 2x categories for that card, making it more like a 3-4% card for me if I used it for all of my spend. However, the best card for you might be very different if your spend pattern is different from mine. The Citi TYP and Amex PRG are also solid choices for my spend (TYP is technically best if I liked all its transfer partners, but I only like Singapore among its partners).
The PRG is not a good grocery/gas card. Technically, the BCP or EDP would be better. If spend is low enough the Sallie Mae can be a great choice as well, but it is not so great for people without Bookstore/Amazon spend and higher grocery spends. If you want an MR card, the EDP and PRG are both choices since they both have bonuses for some of your spend. Do you spend more on groceries or restaurants? Maybe that will answer your question.
The PRG has more prestige than the EDP, but prestige is not something I consider with cards. If you want the minimal prestige you can get with a card someone with 40k income and less than horrible credit (high 600s/low 700s) can get, then sure you can enjoy the prestige. The airline benefit is worth less than its cash equivalent even if you use it. The AF more than compensates for the airline credit ($120 higher AF than the EDP for instance). Therefore, unless you benefit from the PRG bonuses more so than the EDP/BCE/whatever other cards bonus, you should pick another card. Simply put, if comparing the PRG and EDP, even counting the $100 credit, the AF differential puts it $20 behind. Unless it has over $20 (probably more) of a benefit over the EDP in points, the PRG won't be worth it.
TLDR: Look for the card that gives you the best overall benefit and use it if you want a 1 card strategy for efficient rewards. It will never beat out a multicard strategy, but it can be simpler and still reasonably rewarding. Prestige is nice, but unless you are walking around with a Centurion or similar card, any sub-average credit/income individual can likely also get the card. Cards like the PRG are not prestigious as I have seen people with profiles like 40k income and 680 scores getting it on these forums as well as FT.
