My personal preferences depend on what everyone else is doing. I feel characters are defined (almost) as much by what they can do as what they do do. And the mos defining abilities are the powerful, high level abilities. As a wizard what is the mose powerful spell you can cast? As a rogue, how hard can you stab?

Now sometimes losing the higher level abilities can be compensated for in terms of power, by more, good, low level abilities. This can be nice. However, it huts the feeling of being a powerful mage if someone else at the table can cast more powerful spells. It hurts the feeling of being the consumate thief if another sneaks better. If I am playing a wizard and someone else is playing a sorcerer then I am much less likely to multiclass.

On the other hand there are the classes like fighter (in D&D anyway), where the sense of [I]specialism[I] is a bit less clear. There it is taking lots of hits? Dealing lots of damage? Really hard to hit? So many more classes can contribute to the specialism there - even in a game with another fighter I am pretty happy to multiclass as long as it does not diminish my feelings of being a specialist in my chosen area. Feeling to be an effective specialist is more than a raw objective numbers game but about relative expectations.

But whatever, your preferences are, there should be no shame in it. The only way of playing where you should have some shame is if you actively derive pleasure from others enjoying the game less.