The difference in terms of raw survival between RC and BT are pretty minimal. There are mechanics that favor BT occasionally, but outside of those fights they are both perfectly fine. I would give a SLIGHT edge to BT, but they are very close, which is why you see most people just letting personal preference decide. One thing they aren't equal then though is damage output. At low levels of resource generations (like we were in t14/t15) RC does more damage since it offers more B runes (assuming you play BT for death strike, which you should be) and since heart strike is better than death strike for damage per rune, RC will lead to better damage per resource than BT. Once you are in a high resource gen situation though (like we are now with SoB procs on avoidance) damage per execute becomes far more important, and death strike is much better damage per execute than heart strike so BT games for death strike (which you should be doing anyway) becomes the better choice for damage output.
As far as RE being bad goes:
it takes time to dump your rp. at least 1 second per RS. Don't even think in terms of RP, think in terms of seconds. specifically seconds after you dump your FU pairs to dump RP (which you HAVE to do with RE since it only procs on fully depleted runes), which can also be thought of as seconds without an FU pair available.
after 1 second you will have done 1 RS. You have a 45% chance to have 1 F or U rune and a 55% chance to have nothing. meaning you have a 0% chance to have a DS to use.
after 2 seconds you will have done 2 RS. You will have a .45*.45=20.25% chance to an FU pair, and a .45*.55*2=49.5% to have 1 F or U rune, and a .55*.55=30.25% chance to have nothing. This means you have a 20.25% chance to have a DS to use 2 seconds after you dump all your FU pairs a.k.a. 2 seconds where you are guaranteed not to be able to Death Strike unless your other pair is done refreshing.
after 3 seconds you will have done 3 RS. You will have a .45^3=9.1125% chance to have 3 runes back (though any number above 2 runes back doesn't matter since you will have gotten your FU pair, we may as well include it so you can add each of these iterations up to 1 to verify my math if you'd like. if all the possibilities don't add up to 100% then i've done something wrong), and a .45^2*55*3=33.4125% chance to have an FU pair back, a .45*.55^2*3=40.8375% and .55^3=16.6375% chance to have nothing. This means you have a .334125+.091125= 42.525% chance to have a DS to use a full three seconds after dumping all your FU pairs, meaning 3 guaranteed seconds of no DS unless your other pair comes back up.
Remember that you don't always get to wait until your other pair is almost back to death strike unless content is faceroll, and that the base rune regen speed with no haste rating is 7.9365 seconds (not sure how the game rounds internally) WITH full raid buffs.
After 4 seconds you will have done 4 Rune Strikes. You will have a .45^4=~4.1% chance to have 4 back and a .45^3*.55*4=~20.048% to have 3 back (again keeping the values above 2 in here only for thoroughness), a .45^2*.55^2*6=~36.75% chance to have 2 back, a .45*.55^3*4=~29.948% to have an orphaned rune, and a .55^4=~9.151% to have nothing at all. This means you have a .041+.20048+.3675=~60.898% to have a DS to use after 4 seconds of being without without having your recharging pair back.
This means even if you fill every GCD with RS with no delay whatsoever you're statistically going to have to wait a bit under 4 seconds between when you put your FU pairs down and when you get DS again when you use RE. Now, the time it takes to GET the return is about the same for all of them (RE>RC>BT for raw throughtput but all very close. .45vs.405vs.4), but RE is the ONLY one that makes you unable to death strike until you get your return. RC and BT both let you hold on to that pair until you either take damage that requires a DS, or you are about to cap FU pairs. RE doesnt, and forces you to wait until you get your return before you can react with DS again.
So just for a recap there is a:
0% chance you'll have one again before your other pair recharges after 1 second
20.25% chance you'll have one again before your other pair recharges after 2 seconds
42.525% chance you'll have one again before your other pair recharges after 3 seconds
60.898% chance you'll have one again before your other pair recharges after 4 seconds
plus this is all assuming you only use RS for every single gcd until you get return back. Four rune strikes takes 120 rp, so you are also banking on having enough rp generation so that there isn't ANY delay on rune strikes, as well as assuming that you didn't use BB, HS, horn of winter, DnD at any point along the way either.
emember that all this time is time you are GUARANTEED not to be able to react to damage unless you are right about to get your other recharging runes back, which is not something you can count on for progression levels of incoming damage. This ALONE makes RE completely non-viable for blood.