There is a cute argument for $b=c+1$ though I don't know how to pull it through in the general case.
Let $U$ be the set of ordered $c+1$-tuples of sets of cardinality $c$ in which no set repeats. Then, obviously, $|U|=(c+1)!{{n\choose c}\choose c+1}$. Let $V$ be the set of ordered $c$-tuples of sets of cardinality $c+1$ in which no set repeats. Then $|V|=c!{{n\choose c+1}\choose c}$. Now take any element of $V$, i.e., an ordered family of sets $A_1,\dots,A_{c}$. Take any $a_1\in A_1$ ($c+1$ choices). Suppose that $a_1\in A_1,\dots,a_k\in A_k$ are already chosen. Then we want to choose $a_{k+1}\in A_{k+1}$ so that $a_{k+1}\ne a_j$ and $A_{k+1}\setminus \{a_{k+1}\}\ne A_j\setminus\{a_j\}$ for all $j=1,\dots,k$. Suppose that we have $\ell$ prohibitions of the first type. Then, if we honor them, the prohibitions of the second type for the corresponding sets will be honored automatically (if $a_j\in A_{k+1}$ and we don't remove it, then surely $A_{k+1}\setminus \{a_{k+1}\}\ne A_j\setminus\{a_j\}$. The remaining $k-\ell$ sets introduce at most one prohibition of the second type each, so we have $\le k$ prohibitions total. Thus we have $\ge c+1-k$ choices for $a_{k+1}$. Once we run the whole procedure, the reduced sets $A_j$ listed in the same order and the set $\{a_1,\dots,a_c\}$ listed last will constitute an element of $U$ and each element of $V$ will generate $\ge(c+1)!$ different elements of $U$ (by different choices of $a_1,\dots,a_c$. On the other hand, each element of $U$ can be obtained from at most $c!$ elements of $V$ (that is the number of ways to distribute the elements of the last $c+1$-st set among the first $c$. This immediately gives a non-strict inequality you want. To make it strict, you need to assume $c>1$ and $n\ge c+1$ (otherwise you have equality), in which case the ordered sequence of sets $A_j=\{1,2,\dots,c+1\}\setminus\{j\}$ has fewer than $c!$ distribution options (none at all, really) resulting in a legitimate element of $V$.
Edit (the general case)
In this case it will be convenient to define $U$ as the set of all ordered $b$-tuples of sets of cardinality $c$ such that the sets are pairwise different (as sets), the first $c$ sets are unordered, and the last $b-c$ sets are ordered. Then $|U|=b!(c!)^{b-c}{{n\choose c}\choose b}$. Let $V$ be the same as before (ordered $c$-tuples of unordered subsets of cardinality $b$ in which the sets are pairwise different), so $|V|=c!{{n\choose b}\choose c}$.
Now let $\langle A_1,\dots, A_c\rangle$ be an element of $V$. We want to remove $b-c$ elements $a_{j,1},a_{j,2},\dots,a_{j,b-c}$ from $A_j$ and form $b-c$ new ordered sets $B_k=\langle a_{1,k},a_{2,k},\dots, a_{c,k}\rangle$ ($k=1,\dots,b-c$) to get an element of $U$.
To this end start with choosing $a_{1,1},\dots,a_{1,b-c}\in A_1$ in an arbitrary way, which gives $b(b-1)\dots(b-c+1)$ choices. Now, when choosing $a_{k+1,1}\in A_{k+1}$ for $k\ge 1$, add to the standard prohibitions $a_{k+1,1}\ne a_{j,1}$, $A_{k+1}\setminus\{a_{k+1,1}\}\ne A_j\setminus\{a_{j,1}\}$ ($j\le k$), which exclude at most $k$ elements just as before, the prohibitions $a_{k+1,1}\ne a_{1,m}$ ($m>1$), which exclude additional $b-c-1$ elements at most, leaving $c+1-k$ choices as before. These additional prohibitions guarantee that the set $B_1=\{a_{1,1},a_{2,1},\dots, a_{c,1}\}$ does not contain any of the elements $a_{1,m}$ ($m>1$) and, therefore, will be different from every set $B_m$ ($m>1$) as an unordered set and we still have $c!$ choices.
Having constructed $B_1$, we construct $B_2$ with the standard restrictions $a_{k+1,2}\ne a_{j,2}$, $A_{k+1}\setminus\{a_{k+1,1},a_{k+1,2}\}\ne A_j\setminus\{a_{j,1},a_{j,2}\}$ ($j\le k$) and additional restrictions $a_{k+1,2}\ne a_{1,m}$ but now with $m>2$. This gives $c!$ choices again, and so on. Thus, from each element of $V$, we get $b(b-1)\dots(b-c+1) (c!)^{b-c}$ distinct elements of $U$. The recovery of an element of $V$ from an element of $U$ is now possible in just one way, if at all, which, again, gives a non-strict inequality. I leave it to you to figure out when and how it becomes strict in this case.
Best Answer
Here's a combinatorial proof for $$\sum_{k=1}^n k^2 = \binom{n+1}{2} + 2 \binom{n+1}{3},$$ which is just another way of expressing the sum. Both sides count the number of ordered triples $(i,j,k)$ with $0 \leq i,j < k \leq n$.
For the left side, condition on the value of $k$. For each $k$, there are $k^2$ ways to choose $i$ and $j$ from the the set $\{0, 1, \ldots, k-1\}$.
For the right side, consider the cases $i=j$ and $i \neq j$ separately. If $i = j$, then there are $\binom{n+1}{2}$ such triples. This is because we just choose two numbers from $\{0, \ldots, n\}$; the smaller must be the value of $i$ and $j$ and the larger must be the value of $k$. If $i \neq j$, then there are $2\binom{n+1}{3}$ such triples, as we could have $i < j$ or $j < i$ for the smaller two numbers.
For $$\sum_{k=1}^n k^3 = \binom{n+1}{2}^2,$$ both sides count the number of ordered 4-tuples $(h,i,j,k)$ with $0 \leq h,i,j < k \leq n$.
For the left side, once again if we condition on the value of $k$ we see that there are $\sum_{k=1}^n k^3$ such 4-tuples.
For the right side, there is a bijection from these 4-tuples to ordered pairs of two-tuples $(x_1,x_2), (x_3,x_4)$ with $0 \leq x_1 < x_2 \leq n$ and $0 \leq x_3 < x_4 \leq n$. There are $\binom{n+1}{2}^2$ such pairs, so let's look at the bijection.
The bijection: If $h < i$, then map $(h,i,j,k)$ to $(h,i),(j,k)$. If $h > i$, then map $(h,i,j,k)$ to $(j,k), (i,h)$. If $h = i$, then map $(h,i,j,k)$ to $(i,k), (j,k)$. This mapping is reversible, as these three cases correspond to the cases where $x_2 < x_4$, $x_2 > x_4$, and $x_2 = x_4$.
(Both of these proofs are in Chapter 8 of Proofs that Really Count, by Benjamin and Quinn. They give at least one other combinatorial proof for each of these identities as well.)