I'd classify him as a "game delayer". He's an expert at slowing people's farm as they tremble in fear where the next cluster of bombs might be while his own team operates in relative safety.
Rarely will a Techies be the reason you win a team fight (unless they're pushing heavily mined T3's or something), and a gem bought at any phase of the game shuts down his whole plan and arsenal.
This Techies
http://www.dotabuff.com/matches/1154902137
had 7 kills in 12 minutes. I was tired of seeing my teammates feeding him, so I bought a super-fast gem (at maybe 13 or 14 minutes). As you can imagine...he got 2 kills over the next 42 minutes. That's not the mark of someone who can carry you. If he does, it's because the enemy just decided to not play responsible doto and buy sents/gems when needed (before things spiral out of control and your team is behind 10k because nobody can farm safely).
edit: oh and add Slark to that list. Fuck that stupid ult.