Agreed, Matti. This is not one of my favorites, the main reason being George Wendt as the murderer. Notwithstanding his well-known fame for his role as Norm in the hit TV show, "Cheers", he's not a strong enough actor to pull off this kind of part. His weak presence and performance puts a damper on every scene and the entire episode. He can't play sneaky, he can't play angry, he can't play phony sympathetic/upset, he can't play tough. In short, he stinks. He has very limited range as an actor. On top of that, it's kind of difficult to believe a 300-lb guy can effectively disguise themselves. Men of that size are rather rare to see, so to expect him to pull of his bar visit in the cheesy disguise he wore is a bit of a stretch, lighter and drink order notwithstanding.
As to a few of your points:
- Poisoning the Horse: I think he poisons the horse to guarantee the horse loses. And since he'd let on that she "couldn't lose", it prompted Bruno Romano to bet the house on her. When she lost, Romano lost all his money, Teddy was in deep wam-poo and Graham could pretend to "help him out". And pretend to fix things with Romano.
- Measuring the Mouse - I agree - even this seems a bit far-fetched for Columbo to think of right away. I know he keeps up on the police journals (see "Agenda for Murder"), but biology???
The best part of this episode, to me, was Rod Steiger as the mafia boss. He's terrific and would have made a great criminal (he almost is this episode) for Columbo to battle.