Are these two homebrew shields balanced?

I remember being impressed with this question, although it was closed as too broad for asking about too many things in one go. I left a comment at the time about asking less, and coming back to this later, I’ve decided to have a go at asking this. Note that I’ve also taken a look at this question about a homebrew tower shield.

This is partly based on NWN2, a video game that uses 3.5e rules, so I assume shields were broken up similarly in 3.5e, but I only know that game. In that game, there were “light shields” (i.e. “bucklers”), “heavy shields” and “tower shields”.

In short, I wanted to introduce a “light shield” and “tower shield”, keeping the RAW 5e shield as a “heavy shield”. See below for the table comparing AC and pricing, similar to the official table and the above linked question about a tower shield.

$ \begin{array}{|c|c|c|c|c|} \hline \textbf{Armor Name} & \textbf{Cost} & \textbf{Armor Class} & \textbf{Strength} & \textbf{Stealth} & \textbf{Weight} \ \hline \text{Light shield} & 5\,\text{gp} & +1 & \text{N/A} & \text{N/A} & 2\,\text{lb.} \ \hline \text{Heavy shield} & 10\,\text{gp} & +2 & \text{N/A} & \text{N/A} & 6\,\text{lb.} \ \hline \text{Tower shield} & 50\,\text{gp} & +3 & 15 & \text{Disadvantage} & 45\,\text{lb.} \ \hline \end{array} $

In addition to the above table:

  • I wanted it to be possible for the light shield to be donned and doffed as a bonus action (since otherwise why would anyone want it over a heavy shield?)
  • I wanted the tower shield to have the restriction that you needed to be proficient with heavy armor and shields, otherwise you cannot benefit from it and trying to use it imposes the same penalties as with not having proficiency with armor (from Armor Proficiency):

Armor Proficiency. Anyone can put on a suit of armor or strap a shield to an arm. Only those proficient in the armor’s use know how to wear it effectively, however. Your class gives you proficiency with certain types of armor. If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity, and you can’t cast spells.

So, my question is, are my new light shield and tower shield balanced? Meaning, are there any problems from having a light shield that you can don with a bonus action for the cost of -1 AC compared to a RAW shield (what I’m now calling the heavy shield)? Are my restrictions on the tower shield enough to justify basically being able to buy a +1 shield (albeit a nonmagical one), or is it still too strong even so?

(I also considered adding a Strength requirement to the “heavy shield”, like 13 or even just 10, but that kinda screws over Dexterity based medium armor wearing shield users, so I decided against it, but I could be easily swayed into reconsidering it; possibly a separate question to this one, though.)