According to me it goes something like this.
10* - no problem, lots of energy left for next titan.
11* - no problem, since there was a lot of energy left for this one.
11* - problem, no energy left from last one. Flies
10* - Back to the beginning of the “titan rotation cycle”.
Is it normal to let every 3 or 4 titan get away?
The exception is rare titans which are always flasked down if needed.
We chain 13☆ titans. So generally we let fly 1 , the 14☆ .
If the titan is rare its always taken down.
I would say yes, for me experience. I will be glad to know the experience of those fighting 14☆ titans. You hit non stop?
We take down every titan without problems.
Let everry 3rd/4th titan go it’s normal for sure, normally you have some variation with color.
I.E. if the 3rd is a purple and you have a lot of jackal it’s normal to see 80k hits, same thing for red if there many Miki, and this means you will save Titan energy for the next.
I think (almost) all of the top 100 alliances are killing 14* titans with ease and plenty of time remaining. 
At the moment in a top 100 alliance so all titans are chained.
When I was playing in a lower alliance we had the exact same pattern - this is usually 2 runners a week. Which is fine to complete your POV.
Nice ! We can chain easily 13☆ titans but the leader is going through the 1/4 pattern . He say its to save some forge
This is our titan today
Easy question for me. Forsaken Oasis only kills 10 stars and 11 rares.
We could easily string 12s when we aren’t full, and 13s when full but we choose to reserve our battle items and just play our wars seriously.
We manage PoV requirements easily.
On 11* can’t kill 12* just yet and prob won’t for a while. So we let them go unless rare, so basically every time we get a 12* we let it go which is probably every 4-5 titans.
In our Ally we fight 9*, 10* with problems,…usually ± each 5. we let go
We kill 12s easily, but 13s give us a little trouble depending on how depleted we are, what color they are and, to some extent, what time of day they spawn.
So we generally string 2 or 3 13s before w.e. and items are depleted.
I think we are averaging 4-6 before skipping a titan. Especially if skipping one drops us back to 12*.
We try to avoid killing titans in less than 21 hours in the hopes of next titan being same star level.
The thing I like most about my alliance is leadership calls a titan at the beginning so we don’t waste items on a lost titan. We’ve never let a titan go we didn’t plan to. We’ve never let a rare go.
We chain 8s. Almost never let them go unless multiple members are unable to hit.
9s we only take if we killed the last 8 early and have plenty of flags, and if it suits most of our schedules, and we make decent progress on it early on. Otherwise, if it’s down to 11 hours and it still has well above 50% health, that’s a pass.
For reference: we are not a full alliance and many of our members are lower level (below 40). So… that’s why we don’t chain 14*s. Because we can’t. 
My alliance does pretty much the same thing.
We have taken down some 12s, but not often, and never if they’re green (unless it’s rare in which case we flask to the end). We do best on reds and purples, okay on blues and yellows, and a few of us really suck on green.
It also matters what time the titan spawns. If the Americans are asleep when it spawns, we often can’t get enough damage done in time. We’re about half American, a quarter Brits, the rest are other Europeans and then there’s me, the lone Asian.
It is difficult when you’re all spread apart, isn’t it?
My group is mostly U.S., but also a couple in Australia and a few in U.K. / Europe. So it’s like “oh hello, good morning,”
“You mean good night? I was just headed off to bed”
“Oh, right, right.”
Half the time, we’re not even all playing on the same day, apparently.
“Happy Friday!”
“It’s Saturday here…”
“Oh @#$%.”
My alliance takes good advantage of being worldwide. It means someone is always awake if a titan needs an extra push at the end.
That is a definite upside for sure, and I’m happy to have international members (not just for that reason).
Still, even with us being spread apart, sometimes the titans spawn at bad times for all of us. Like half the team is asleep and the other half is at work. Doh! 
The 8*s though are almost always manageable for us, even if no one is able to hit it for the first 6-8 hours. Because eventually people start waking up and coming home from work and boom that titan can go from full health down to 50% in a couple of hours.
9 stars for us though are just… ugh. Overall, we average about 100k damage per member per titan on 8 stars, and we only have 22 members (now 23, new addition as of yesterday)… our average damage on 9* titans tends to be at least 10-20% lower than our damage on 8s, and 9* titans usually have more than 2.3 million HP, so…
I’m sure there are some members in my alliance who don’t like it when we let the 9 stars escape, but for me it’s a case of simple mathematics. We simply cannot afford to flask every single 9 star into eternity… and then what happens when we move up to 10s? It’s simply inevitable that we’ll eventually have to let one go.
