Currently at the end of my second campaign, my fleet has 2 Onslaught XIV and 1 Mora. These are worth 100 DP, while other military ships are worth 160 DP, including a Paragon and an Odyssey. Granted, all frigates are high-tech: 1 Hyperion, 1 Scarab, 4 Wolves. Also 1 Medusa.
Earlier during that campaign, I had an Enforcer (which I kept a long time), 2 Condors (replaced by Mora quite early), 1 Dominator XIV and 1 regular Dominator (replaced by first Onslaught XIV). So personally I consider low-tech viable up to this point, and I mix all tech types differently depending on mood and what ships I obtain after battle and while shopping.