All units besides marines have lower amp assult, there are now transport and landing craft, tps can only rebase to major ports
That is not precisely true, actually amphibious landing bonuses have been shuffled around so that a bonus actually come with 1936 infantry tech, and this value was removed from Marine tech. They are basically the same bonuses as in vanilla, they have just been moved.
This is to allow powers without a real amphibious landing capacity (early war, or land based powers) to have some amphibious capability, even if they don't research marines. Still marines, and marine tech are essential to creating a real naval power, but early war Japan does have some ability to land against those Chinese divisions with infantry or mountain troops, and USSR could potentially land against a weakly defended Baltic coastal province, without having advanced marine tech.
That is the idea anyway.
This was done because in earlier versions of the mod, invading was extremely difficult against beaches even defended with one unit, given the length of combat time, the ability to use support defense more effectively, and the increased intrinsic defensive strength of units.
For the same reason, we also allowed for larger invasion forces earlier, increasing the amphibious stacking limit. For example, in vanilla "Base Strike" increases the stacking limit to 4, while in EIR it is 6.