Are you speaking as a Thinkorswim client or as an Ameritrade client? I'm of the former and I have not had any lags recently. Ironically, I had to switch to TOS when the Zenfire feed lagged all last week. I might be wrong, but I don't think the TOS platform provided by Ameritrade has the same backbone as the one offered by Thinkorswim. How long have you used TOS? Although I've not used every damn software out on the market, TOS is one of the better (read: reliable) platforms I was lucky enough to encounter only last year. Perhaps you don't really know what you're talking about?
You are correct. ToS uses S&P Comstock as the data-provider. I am also aware that Ameritrade uses DTN, among others. There is a lot of redundancy out there. To claim otherwise is to be highly naive.
This is my 2nd on TOS thru TD. Market Internals seem to be almost perfect synch with my DTN IQ paid feed. I had to call tech support because the default setting is 3 second delay, now on real time.