A few points about this.
1) easyJet offloads an average of 14 bags per flight
2)
AFAIK nobody is stopping the use of the overhead lockers. It says it should fit under the seat. That means in theory there should not be any need for offloads due to running out of space in the cabin. Offloading cabin bags is a big source of customer dissatisfaction.
3) You can't pay extra for the larger cabin bag which would be profiteering.
4) The extra legroom/up front seats also gets you the larger cabin bag size plus a smaller bag and priority boarding
5) If you fly at any frequency the easyJet plus membership gets you all this for a fraction
6) Flexi fare customers get all that as well as fast track security and some complimentary food/drink
7) Standard seat passengers can still bring the larger bag and use "Hands Free" for £7. "Hold baggage" gives you two options. 15kg and 23kg
8) Those an easyJet holiday get 23kg hold luggage included
9) Failing all that, the new standard cabin bag size bag dimensions are larger than you think.