MPLS access links would normally use a point to point circuit anyway.
MPLS proper is the "cloud" bit operated by the carrier
in most setups the label switching bit is only within the carrier core network, and will not go as far as a customer site - so they could be plugging all those access links into a central router instead....
some services do - it sounds like you are referring to a L3 VPN over MPLS.
But some MPLS services across are point to point - Ethernet L2 circuit emulation is common.
The access links to / from a customer site run IP, so no difference.
The MPLS core QoS field inside a label is only 3 bits, so the "native" per packet QoS is less rich than say DSCP.
Since the backbone tends to be much faster than customer access links that may not matter (as if you never have packets building up in a Q there is not much QoS can do to re-order traffic).
Some MPLS backbones dont do any QoS handling in the core, but just at the PE router where customer links meet the high bandwidth bit, since it is sometimes simpler and easier for the carrier to throw bandwidth at the problem