"Triscend produces the E5 serie which has a poor MCU core"

What do you mean by "poor?"
It is precisely an MCU core - nothing more, nothing less!

"a biting irony of the choise is that with E5 serie and its SLC [sic?] I can make hardware similar with that Cygnal chips have inside."

I presume you mean "CSL" there - Configurable System Logic.

That's not irony, that is the whole point of the device!
The Configurable Logic lets you implement precisely the set of peripherals you require, rather than trying to find the nearest match from standard parts.

Two key criteria that could make Cygnal your better bet would be:
1. Analogue: The Triscend has no on-chip analogue stuff;
2. On-Chip Flash: The Triscend does not have on-chip flash.
If either (or both) of them is critical to your application, that'll obviously rule out the Triscend. :-(

Unfortunately, I don't know the Cygnal parts well enough to say which Triscend features would rule out a Cygnal.
I s'pose if you needed 10 UARTs, that would be one?
The extreme flexibility of its memory interface could be another, and the sheer volume & flexibility of IOs?

As well as the JTAG, the ability to run your code from the on-chip RAM or off-chip memory of any flavour (RAM, Flash, whatever) at the mere switch of a config option is an absolute boon!