Your idea would be good in deep space.
The correct answer is "it depends" and "because that would damage the network as a whole". TCP/IP is very kind to networks and automatically adjusts to about the right speed to be fast but not generate tonnes of ICMP return packets.
When a router with not enough RAM suddenly receives a lot of any kind of packet - say from Tsunami, Bittorrent or FDT - it drops it and fires back to the sender a small failure dis-acknowledgement packet. Now your UDP server has to track and re-transmit that part manually. Some ISP routers shape Bittorrent so many this hurts Tsunami?
The Tsunami protocol uses UDP with a control channel in TCP. http://tsunami-udp.sourceforge.net/ I found a study which shows it to be slower than a thing called FDT.
The legendary Fast Data Transfer (FDT) protocol from CERN is capable of saturating any network using multiple TCP streams. Probably it is faster, because it causes less re-transmits that Tsunami, which floods the network with so much UDP, some of it does not make it all the way across.
UDP is used by unreliable applications: streaming audio, game input/update IO, "ping" is actually ICMP but is not guaranteed, Bittorrent, mosh ssh is awesomely responsive, VOIP telephony, multicast, DNS is sent over UDP AFAIK. Anything that does not mind the odd missing packet and can "catchup" instantly.
TCP/IP was really the killer invention that allowed app devs so just set and forget. A socket is a pair of IP address and ports, and were designed to be able to be setup and remain for hours, days, even weeks without re-connecting. Email, web, IRC and literally all the killer apps use TCP. But you can get strange pauses in the download that suddenly go faster... and in deep space the connections may time out making Tsunami style transfers best for interstellar file transfers - you could be onto something there!!
The proof is in the final remarks of this science study extract, which mention the increasing distance thing I'm going on about re: deep space
Without congestion, performance of FDT and GridFTP with TCP is higher
than Tsunami and UDT. The highest through- put of FDT is 2.34 Gb/s
with a 1 ms RTT but it decreases rapidly after 100 ms compared to
GridFTP, which performs better than FDT when link RTT is longer than
100 ms. Interestingly, the throughput of Tsunami did not decrease
over increasing RTT, showing it has the most effective congestion
control with increasing RTT.
Then again... there is actually a space protocol that is a lot like email which would be better for space. The apps have to not mind time-out values such as forever.