I'm going to agree with raynard and others but to a step further. The really bonkers prx combos tended to require very narrow very specific feat chains and occasionally painful skull choices. They simply were not that big of a deal because they were so obvious and the gm could ask why Bob is investigating so heavily in $wierdSkill then plan for it or shoot it down. 5e does away with all that in order to lower the bar far enough to ensure abserd is both trivially possible and effective with a multi attack matching straight fighter thanks to one of those classes.Its odd folks worry about this. Even in 3E it was fine. It was prestige classes that were an issue.
high levels can get broken real fast.Always. We recently finished a campaign at level 20 that I honestly hated for the last six months. Going back to level 1 and generally to lower levels is very refreshing. Completely different emotions and problems. I really missed that.
I think it's because...Right. I don't mean "Why is there a first level?" I mean "Why is first level training wheels?" 5E is the only edition to ever do that. Obviously character got more powerful and more complex as they leveled in previous editions, but no edition besides 5E has said "Character generation isn't done until 3rd level." It is kind of bonkers.
There is an easy solution to that: eliminate it.
I don't think you need to entirely eliminate it. Just eliminate the dipping. Either you're a rogue/cleric hybrid from the start and keep them at equal levels, or you're a 7th level rogue who decides to become a cleric, and you have to spend your next 3 (or so) levels on that before you can choose which class to level. Or, heck, make the so-called "tiers of play" a more formal structure, and you can only change classes on a per-tier rather than per-level basis.I think multiclassing is a huge mistake.
Or, yeah, a proper Gish class would greatly reduce the demand for multiclassing.Dipping for class features via multiclassing is the problem. Just make a Gish class.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.