Why not? 1st & 2nd level abilities are, by definition, class- or archetype-defining but not especially powerful. Any combination of the same might end up having more synergy tan intended, but I'd be shocked to find anything game-breakingly powerful.
I mean, by the last time I counted 3.5 had something close to 50 base classes available by the end of the run. Name me a low-level multi-class combination from that edition that was more powerful or game-breaking than taking another level of Cleric or Druid. Without depending on a feat or magic item combination. I'm no CharOper by any means, but I can't really think of anything. Once again, class bloat did not really contribute to 3.5's power creep in any significant way. And 5e makes multiclassing cost more than 3.5 did.
But more important to that is my final point, which is this. Say that, due to unintended synergy, Butler 2/Dandy 3 is, strictly speaking, better than your Life Cleric 5. I have to ask... so what? What does it matter, in the long run? Don't forget that the Cleric as an ASI/Feat at this point, which makes a difference.
Look, CharOpers are going to CharOp. Other tables are only going to build PCs in the way that makes sense to them in-character. BOTH of these types of players benefit from more options, more classes, more multi-classing. I don't see a compelling argument for restricting it to one or the other.