Cool.
Is it true that interdictions are always escapable, or, alternatively, is it true that Open carries more risk than Solo?
Unfortunately, like most things in life, it isn't that simple.
The first question: "Is it true that interdictions are always escapable"
The answer is no, not all interdictions are always escapable.
Player GoodGuy is flying a shieldless sidewinder that does not have chaff.
Player BadGuy is flying a fully engineered clipper with all gimbal frag cannons.
If BadGuy interdicts GoodGuy, GoodGuy is going to die nearly 100% of the time to BadGuy. Regardless of BadGuy's skill (as long as they reasonably know how to play the game).
And that is going to go for probably any ship GoodGuy flies if it is shieldless without chaff.
Now if GoodGuy uses a reasonably defensive build on their ship, follows some basic piloting tactics, then yes, nearly all interdictions are escapable. As long as GoodGuy's ship can survive 15 seconds, they should get out alive. However, if you get hit with an FSD reboot missile, you will need to survive a bit longer, so the more defensive the build, the better. There is also the chance that GoodGuy makes a mistake. Mistakes against players are much more deadly than mistakes against NPC's.
Reasonably defensive build does not mean full on PVP ship. A decent sized A-rated (or prismatic) and some shield boosters is what you want. Throw in some basic engineering and you are even better off.
So for the 2nd part: "is it true that Open carries more risk than Solo"
The answer is yes, but the CMDR can take steps to address the additional risk.
Using CG's as an example.
GoodGuy can fly a shieldless cutter in solo/pg to a cargo CG and be reasonably free from exploding and just fly station to station delivering cargo.
In open, GoodGuy needs to sacrifice cargo space to raise their odds of survivability. GoodGuy will also need to fly evasively in supercruise to try and prevent interdictions in the first place. And if interdicted, will most likely need to leave the system, then come back and try again.
So lets say GoodGuy's chance of survival (not seeing the rebuy screen) are the same in open vs solo/cg. But if GoodGuy was flying in solo, he/she would be able to do many, many more deliveries for the CG.