I think Eugene has hit the nail on the head. I don't think it's really worthwhile to make the assumption that you'd be guaranteed E+, because that won't always happen.
MRTC = more room for all seats and all pax; E+ = more room for some seats and some pax. While people say there's more room in E+ than MRTC, the difference is not significant enough to me that I'd want to be bothered having to worry about whether I'll get an E+ seat.
Note this is my opinion only and that I've never actually had the opportunity to fly E+.
FewMiles..
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