In terms of portability and convenience, you can’t really beat Eurorack. Also if you’re into concrete - it’s hard to beat the number of tools available in Eurorack. I personally love the Morphagene, Mimeophon, and Erbe-Verb when doing that kind of thing.
One nice thing about the Easel unlike other choices is that you’re getting a complete instrument. It’s very portable and quite easy to combine with some Eurorack modules to expand the palette - Todd Barton has many great demos of this combination if you’re looking for some inspiration. I have access to one in my studio, I’m by no means an expert, but it’s a really great system with tons of possibilities.
I love the R*S Serge eurorack modules. I also have access to a R*S 4U XL boat system, working with bananas is lot of fun - but personally it’s not enough for me to get to rid of my Eurorack Serge and switch over.
Having tried all these different options - my opinion is that there’s not much of an interesting vs. discussion. They all sound different and bring something special to the table.
Based on what you’ve said, I think the important quality that you’re looking for is that of unified instrument - thus this leaning towards an Easel or a setup from one manufacturer. I would say go with that instinct.