Understanding GSM BTS Tx power levels

[Mychaela Falconia]

Hello GSM network side community,

I am doing some research in preparation for possibly setting up my own
GSM/2G BTS in my rural town of Middle-of-Nowhere, California to serve
as a replacement for our current GSM/2G service provided by T-Mobile
USA, a contingency plan to be activated if and when the evil corporate
owners of T-Mobile shut down their 2G service.  I haven't bought my
BTS hardware yet - I am still doing research and comparing options,
and I also need to do some other preparatory work without which the
BTS won't be of any use.

I have a question about GSM BTS Tx power levels.  Some BTS vendors
advertise models with up to 10 W power output, but I don't understand
how such high power output from a BTS can be useful when MS power
output in the other direction is limited to 1 W in high bands or to
2 W in low bands.  The whole point of a BTS is to provide service to
subscribers, and in order for a subscriber to be able to make a call
or to engage in a text conversation, there has to be two-way
communication between the BTS and the MS: the MS needs to hear the
downlink signal from the BTS, and the BTS needs to hear the uplink
signal sent by the MS.  If you have a BTS that puts out 10 W on the
downlink, wouldn't the effective range be limited at the point where
the BTS can no longer receive the 1 W (high bands) or 2 W (low bands)
uplink put out by the MS?  And if the range limit is set by the Tx
power limit of standard GSM MS units, what is the point of having the
BTS put out more power on the downlink than the very same 1 W or 2 W
limit that applies to uplink Tx power?

I can only reason that I must be missing something big here, as those
BTS manufacturers who offer models with 10 W output surely make such
hardware for some very valid use cases - but I would like to understand
it better.  Can someone perhaps explain this mystery to me?

TIA,
Mychaela