Launching the first tier of a new animal/plant makes a lot of fun. But the higher tiers are just disappointing shit.
1.) They are completely unbalanced. Some need 1 hour to breed, others need a week. And I don't talk about luck, I mean ingredients. Fish and Fawos are a nightmare.
2.) It's random shit. You have a 0.5% chance (higher tiers only 0.3%) to get a higher tier egg/seed/whatever. This mean it can take 10 seconds, or it can take weeks.
3.) It's possible to ruin your breed. When you get your 0.5% egg after endless time, you have to hatch it. Unfortunately many recipes give a rather high chance that the egg just dies. Start over again. Or just load a save.... That's what I call fun.... not.
4.) Some species need cross-breeding ingredients. Xyhip MK2 needs fish MK2 and Fawo MK2. Already burnt all your MK2 Fawos because you are already at Fawo MK3? Bad luck for you.
5.) And the most important thing: You don't need them at all. You can have the same effect by building one more farm. This effectively means you only do it when it makes fun to do it. Unfortunately it doesn't.
Suggestion: Make breeding much easier. Give 3% chance flat to every tier. Remove cross-breeding. Make sure they give a fair benefit. Some farms get a big boost (for example auogs) while with others it's just a joke (for example cadaveric, yaedols).