It is not an strict imbalance, but I think Pikeman base compares poorly with Penguin++ (Pikeman has its passive and attacks instead of freeze, but penguin++ can move horizontally witout help, defend back squares and still threaten the same forward squares as Pikeman at the same price)
I would argue that pikeman is better than penguin++ as freeze is much worse than attacking on a low cost piece especially when the both pieces' primary use is defense, a role forced by poor mobility as worst case scenario you trade with the piece best case is you have enough attackers on the square to take it for free. Freeze's primary purpose is to give extra time so you can take it for free or take it with a cheap piece. However you can't take a piece much cheaper than 2 and the risks are fairly large considering that your opponent can outtempo you fairly easily if you aren't careful and force you to lose material. That said both have their place but in many situations pikeman is better than penguin++.
Freezing in your own side of the board is underrated because it keeps the enemy piece blocking that square and it delays an unstoppable attack (I am biased because that is what I have to defend against on most of my games), whereas killing may end up in an unfavourable trade, and pikeman will be mispositioned if killing on the diagonals, but I see your point regarding an inmediate threat and not losing the ability to capture because of your opponent creating new threats when something is freeze, so maybe it is just that I am biased by my specific games and Pikeman is better in general, whereas Penguin is more situational (still, I think when pikeman takes on its diagonals it loses its defensive capabilities)
It's worth noting that penguin++ is currently the least used unit in the game, and has been considered 'extremely weak' for a very long time in the cycle form it shared with bombers, so if it becomes debate-ably stronger than pikeman for certain strategies I think that's actually a good sign and matches the intended purpose of the change.
Supposing the penguin buff is overcompensation, I think it's still unlikely to result in major problems since stacking multiple sources of freeze has diminishing returns (especially when the targets overlap), compared to stacking more attacks which helps to win trades.
I totally agree, new Penguin is not OP by any means, and it coming back into the game relatively strong is great.
I just say that pikeman base may be a bit overpriced now (but at 1 cost it would probably be way too cheap so it is okey), but this is a minor problem compared to penguin needing that buff.