A Saito 56 would fly this model well, but it would not have any reserve power. My pal's has a YS 63, which is equal in output to your Saito 72 (practically speaking). Unlimited vertical, etc., etc...

Do not let this one bad experience sour you on four-bangers. While I have only owned one Saito, the 72 is one of their better ones. You could indeed have one that has a bad out-of-balance crank, or whatever.

You could also have an airframe problem (broken motor mount, cracked firewall, etc.) that is not readily apparent.

Four strokes are cool. They do take a bit more attention than two strokes, but sacks full of people find that extra effort more than worth it.

I would try your engine on another airframe (a test stand would be too rigid for you to really notice what's going on) to see if it shakes that one as bad. If so, send it back to Horizon with a detailed letter of explanation. They have an excellent track record regarding standing behind their products. If not, then you know to scrutinize your model more closely.

The early 72s had a problem with busting the crank case. This was due to insufficient strength in the case webs to handle the increased power output. That has supposedly been addressed. The fact that there are many, many happy users of this engine speaks for itself.

If you blow off four strokes because of this bad experience, then you might be robbing yourself of some additional modeling enjoyment.