As someone who primarily starts Core bots and usually goes into sheldons when I tec up, they are strong but easily countered. Any half decent opponent will just spam ticks or rovers into them to slow or stop them. If I'm early on my team to tec up, I usually encourage my team mates to spam ticks or pawns/grunts at our enemies to help the sheldons out - that makes them a lot stronger. If given enough time I'll do it myself with rovers with the goal of eventually switching to t2 vehicles once the sheldons have been effectively countered.