What you have learnt in electromagnetic course is valid of course

i think you are following the right definitions to get the understanding but you are missing important facts

so in order to understand you need to keep in mind these facts :

1-For the back emf to exist it needs a change in the magnetic flux to happen :that change has to happen before the back emf develops

2-The voltage source has always and advance on the back emf what that means is the back emf does not develop instantaneously when the source is connected , the back emf takes a delay to develop(that`s the lag you see in ac inductive circuit) but we tend to forget about it in DC

3-an opposing equal force does not mean necessary a decreasing flow (speed mechanically , or current electrically) in the system itself, it decreases the original flow that would have to happen if the inductor or inertia was not there and depending on what the system is you get a constant rate change (constant acceleration ) if the system is an inductor, or a constant flow (current/speed ) if the system is a dynamic resistor, no flow if the system is a static resistor (a non conductive material is kind of static resistor ,you need a breakdown voltage to get through it and transform it into a dynamic resistor)

before taking an attempt in explaining the current behaviour in your circuit above before t=0 at t=0 and after , recalling some analogies will be useful:

The third law of newton in mechanical systems is a lifesaver and still valid for electrical systems by analogy:

where mass (inertia) is equivalent to inductance L dynamic resistance is equivalent to the Resistor R Static resistance is equivalent to non conductive material which requires a breakdown force to overcome the static force Stiffness K is equivalent to the capacitor C

Let a system subject only to it`s own inertia (mass) with an external force F acting on it ,we get the following equilibrium equation:

F=M*a where a is the acceleration or the rate at which the speed of the system changes over time

This equation shows that for M*a to develop a change in the system creating the "a " has to occur so a change in the initial speed of the system has to occur.

The initial speed is zero, so as long as F is not there ,no change in the speed occurs and a is zero so Ma is zero and no back opposing force is developed Now We introduce F to act on the system M , F has an immediate effect and starts pushing on M ,if the system was massless it will accelerate it with an infinite acceleration and hence it will gain an infinite speed but because M is there it can only push a little amount immediately so that at t=0+dt the Mass would gain a limited speed of 0+dv ,even if we make dt the smallest possible (epsilon), the dv will also be smaller so that the di/dt is always constant and defined by the M value Now Ma will develop to oppose F but this opposing force takes time to appear (not only the dt inherent to the creation of "a" but a real lag behind F, that's the famous inductor lag which is responsible for example for the slip in the induction motor ), Ma is always chasing F during that time F will push another amount of speed in the system with dv/dt being always the same so V increases as Ma is only generating the first deviation dv for now which is the new steady state for M , but as F pushed a new amount and V increased again ,M again keeps developing an M*a to oppose the new change which is now the new dv pushed by F ,or it is (the new dv plus the old dv)-the old dv = the new dv , and again during that time F pushes a new amount dv in the system etc etc etc ,and dv/dt stays always constant which means the system increases its speed with a constant rate . If you remove F now , a becomes zero which means the system will keep its last speed as a constant and keep moving at this speed unchanged till a new force tries to change it .

If the system had a dynamic resistor , that would only change the maximum original speed vmax that F can Push so the inductor still limits the change but only up to the maximum value allowed by the resistor and then you get constant speed as if you only had the mass with F=0 ( which is true as here R*Vmax completely opposes F)

Now for your example just replace the speed V by the current I and you end up with exactly the same behaviour .

You can also reason using the external original maximum speed trying to push through( as M opposing the maximum speed rather then the pushed amount of speed into the system but always keeping in mind that F has and advance ) instead of the internal system speed you will come to the same conclusion.

Another tool that really is powerful in understanding how the power flows in different systems with different characteristics (stiffness,resistance,inertia) is bond graphs, it always works with flow and force whatever the system is mechanical (force is the mechanical force and flow is current),hydraulic (force is pressure and flow is the hydraulic flow ,electric (force is electric potential and flow is current ),thermal (force is temperature and flow i dont remember what was that ) , unfortunately it has been a while since i have studied it and used it so i dont remember well the principles to use it but i know for sure it is a powerful tool to understand the exact flow of power/energy in the system , what goes into what and how including transformations, if you can spend some time on understanding it,it will help you understand and solve this kind of problems