Radio level integration (RLI) architectures such as LTE Wi-Fi aggregation (LWA) and LTE Wi-Fi integration with IPSec tunnel (LWIP) are gaining momentum in the context of Multiple Radio Access Technology (Multi-RAT) connectivity in 5G. It is unclear whether a transport layer solution like Multipath TCP (MPTCP) could serve better in aggregating multiple RATs than radio level aggregation, Or are these two different solutions complementing each other? In this paper, we address these questions by experimenting on a testbed. LWA testbed has been set up using OpenAirInterface (OAI) LTE base station and off-the-shelf Wi-Fi Access Point (AP). We present interesting outcomes of various experiments which can be adopted as design principles for developing 5G Multi-RAT architectures. Our findings include, (i) LWA fails to aggregate link capacities when there is congestion in the network, and (ii) Co-operative MPTCP and LWA solution is robust and achieves significant performance improvement compared to individual LWA and MPTCP, even when the network is congested and Wi-Fi channel contention is high. © 2018 Association for Computing Machinery.